Guayule with increased rubber production and yield

ABSTRACT

Altered guayule that produce more rubber than the amount of rubber produced by non-altered guayule are provided. The alterations may include (i) a reduction in amount of functional PaAos produced by the altered guayule, (ii) an increase in amount of a transcription factor produced by the altered guayule, (iii) an increase in amount of salicylic acid within the altered guayule, (iv) exposure of the altered guayule to cold temperature, and (v) a combination thereof. Methods of producing the altered guayule and methods of increasing the amount of rubber produced by a guayule are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. patent application Ser. No. 15/975,851, filed May 10, 2018, which itself claims priority to U.S. Provisional Patent Application 62/504,762 filed on May 11, 2017, contents of which are expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION Sequence Listing

The Sequence Listing submitted via EFS-Web as ASCII compliant text file format (.txt) filed on Mar. 10, 2021, named “SequenceListing”, (created on May 9, 2018, 50 KB), is incorporated herein by reference. This Sequence Listing serves as paper copy of the Sequence Listing required by 37 C.F.R. § 1.821(c) and the Sequence Listing in computer-readable form (CRF) required by 37 C.F.R. § 1.821(e). A statement under 37 C.F.R. § 1.821(f) is not necessary.

Field of the Invention

This invention relates to altered guayule plants that grow larger and produce more rubber than non-altered guayule plants, when grown under the same conditions. The altered guayule contain the cDNA sequence of Parthenium argentatum Allene oxide synthase (PaAos) in the reverse complement orientation under control of a heterologous promoter which reduces the production of PaAos via RNAi. Other types of genetic alternations can be made in guayule to reduce the functionality of PaAos. Methods of increasing rubber yield in guayule via reducing PaAos translation and/or reducing the amount of functional PaAos in plants are also included.

Description of Related Art

Natural rubber is synthesized by more than 2,500 plant species (Cornish, et al., J. Nat. Rubber Research 8:275-285 (1993); Cornish, K., Phytochemistry 57:1123-1134 (2001)). Rubber is produced by these plants as a secondary metabolite with no clear indication of its function in plant cells. Possible reasons on why these species synthesize rubber are to defend themselves against pathogens and insect attacks, repair tissue damages caused by mechanical wounding and protect cell damage induced by environmental stresses (Demel, et al., Biochim. Biophys. Acta. 1375:36-42 (1998); Tangpakdee and Tanaka, J. Rubber Res. 1:14 (1998); Vereyken, et al., Biochim. Biophys. Acta, 1510:307-320 (2001); Kim, et al., Plant Cell Physiol., 412-414 (2003) and references therein; Konno, K., Phytochemistry, 1510-1530 (2011); and Sarkar, J., Rubber Science, 228-237 (2013)). According to a 2014 market report, the rubber that these plants produce accounted for $16.5 billion in trade worldwide (rubberworld.com/RWmarket_report.asp). Even more so, the end products made from natural rubber, including tires for the transportation industry, sports equipment, medical devices, and more, are indispensable in our everyday life. The Hevea tree is the main source of natural rubber but concerns exist as it is limited geographically to tropical climates, mainly in Southeast Asia, is susceptible to diseases, and produces rubber that causes allergic reactions. Clearly, an alternative source for the production of natural rubber is very important to reduce economic risk and safeguard human health.

One plant known to be a promising source of natural rubber is guayule (Parthenium argentatum, Gray), a desert shrub native to the southwestern United States and northern Mexico (Mooibroek and Cornish, Appl. Microbio. and Biochem. 53:355-365 (2000); van Beilen and Poirier, Critical Reviews Biotech. 27:217-231 (2007)). The majority of rubber synthesis in guayule occurs during the cold season. Guayule synthesizes rubber within subcellular organelles called rubber particles (Archer and Audley, Bot. J. Linnean Soc. 94:181-196 (1987)) stored in the parenchyma cells of stembark tissues (Gilliland, M.v., Protoplasma, 169-177 (1984)); Macrae, S. G., Plant Physiol., 1027-1032 (1986)). Natural rubber synthesis is initiated by the action of allylic pyrophosphates initiators (Cornish and Siler, J. Plant Physiol., 301-305 (1995)), usually farnesyl pyrophosphate (FPP). Then, the monomer isopentenyl-pyrophosphate (IPP), produced by the mevalonic acid pathway (MEV) in the cytosol and the methylerythritol phosphate (MEP) pathway in the plastid (Mooibroek and Cornish (2000); van Beilen and Poirier, TRENDS in Biotech., 522-529 (2007)) elongates the rubber chain. Rubber synthesis is mediated by rubber transferases requiring magnesium ions as cofactor (Da Costa, et al., Phytochemistry 67(15): 1621-1628 (2006)).

The proposed model for the structure of rubber particles consists mostly of hydrophobic cis-polyisoprene units (natural rubber) encapsulated inside a protein and phospholipid surface monolayer (Nawamawat, et al., Colloids and Surfaces A: Physicochemical and Engineering Aspects, 390:157-166 (2011); Sansatsadeekul, et al., J. Biosci. and Bioeng, 111:628-634 (2011)). The phospholipids serve to stabilize and solubilize the otherwise insoluble (rubber) product. Guayule rubber particles include several proteins (Whalen, et al., Development of crops to produce industrially useful natural rubber. Chapter 23 in Isoprenoid Synthesis in Plants and Microorganisms: New Concepts and Experimental Approaches, Bach and Rohmer (eds.), DOI 10.1007/978-1-4614-4063-5_23, Springer Science+Business Media NY, 329-345 (2013)) of which Aos has been found to be the most abundant (Backhaus, et al., Phytochemistry 30:2493-2497 (1991)). Aos is well-known as an enzyme in the jasmonic acid biosynthetic pathway (Harms, et al., Plant Cell, 1645-1654 (1995); Wang, et al., Plant Mol. Biol., 783-793 (1999); Schaller, F., J. Exper. Botany, 11-23 (2001)). The role of Aos in rubber biosynthesis, and the reason for the abundance of Aos protein on guayule rubber particle surfaces, is not known (Whalen, et al. (2013)).

The need exists for a method to increase rubber production in altered guayule compared to rubber production amounts in non-altered guayule in order to improve the commercial attractiveness of using guayule rubber as a replacement of synthetic rubber and Hevea rubber. Further, a need exists for increasing the rubber yield per acre obtained from altered guayule compared to the rubber yield per acre obtained from non-altered guayule. This greater rubber yield results from the altered guayule being larger in size than non-altered guayule of similar age. A need also exists for altered guayule that produce more rubber than the amount of rubber produced by non-altered guayule. A need also exists for altered guayule that have a larger size than similarly aged non-altered guayule because the altered guayule that are larger than the non-altered guayule will possess more tissue for storage of rubber and thus generate greater rubber yield per acre than the rubber yield per acre of non-altered guayule.

BRIEF SUMMARY OF THE INVENTION

It is an object of this invention to have an altered guayule (and progeny and parts thereof) that produces more rubber than the amount of rubber produced by a non-altered guayule. It is a further object of this invention that the alteration causes the altered guayule to produce a reduced amount of functional Parthenium argentatum Allene oxide synthase (PaAos) compared the amount of functional PaAos produced by non-altered guayule. It is another object of this invention that the reduced amount of functional PaAos causes more rubber to be produced by the altered guayule compared to the amount of rubber produced by non-altered guayule. It is another object of this invention that the reduced amount of functional PaAos causes the altered guayule to grow larger in size compared to the size of similarly aged non-altered guayule, and the larger sized altered guayule has an increased rubber yield per acre than the rubber yield per acre of similarly aged non-altered guayule. It is another object of this invention to have an altered guayule that produces a greater rubber yield per acre than the rubber yield per acre produced by a similarly aged non-altered guayule. It is a further object of this invention to have germplasm, pollen, flowers, seeds, stems, leaves, roots, cells, etc., of the altered guayule.

It is an object of this invention that the altered guayule contains an alteration in PaAos functionality. It is another object of this invention that the altered guayule contains an expression vector which further contains a heterologous promoter operably linked to a polynucleotide encoding PaAos anti-sense RNA and/or PaAos dsRNA and/or one or more guayule transcription factors, PaWRKY3-like (SEQ ID NOs: 39 and 40 and a sequence at least 95% identical thereof), PaWRKY71-like (SEQ ID NOs: 41 and 42 and a sequence at least 95% identical thereof), and/or PaMYBS3-like (SEQ ID NOs: 43 and 44 and a sequence at least 95% identical thereof), for overexpression of one or more of the transcription factors and/or the anti-sense RNA or dsRNA. It is further object of this invention that salicylic acid (SA) and/or PaAos dsRNA is administered to a non-altered guayule to make an altered guayule that produces more rubber than a non-altered guayule. It is another object that an altered guayule (containing one or more of the following: one or more expression vectors encoding PaAos anti-sense RNA, PaAos dsRNA (SEQ ID NO: 45), PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like) is also treated with one or more of SA, PaAos dsRNA, and/or cold temperature (between approximately 7° C. and approximately 15° C. for approximately 8 hours per day), thereby causing the altered guayule to produce more rubber than is produced by a non-altered guayule and have great rubber yield per acre than non-altered guayule. It is a further object of this invention to have methods for creating the altered guayule. It is a further object of this invention to have altered guayule and parts thereof created by those methods.

It is an object of this invention that PaAos anti-sense RNA has a sequence that is the reverse complementary sequence of PaAos (SEQ ID NOs: 9, 12, or 14 or a sequence at least 95% identical thereof or any PaAos sequence in any guayule cultivar) or a fragment thereof (e.g., SEQ ID NO: 11 or a sequence at least 95% identical thereof, or any 19 contiguous nucleotides of SEQ ID NOs: 9, 12, or 14 or a sequence at least 95% identical thereof or any PaAos sequence in any guayule cultivar), such that the PaAos anti-sense RNA silences PaAos via RNAi in the altered guayule. It is another object of this invention that the dsRNA (either produced by the altered guayule or administered to the altered guayule) is at least 19 nucleotides long and contains a sense region selected from a portion of SEQ ID NO: 11 or a sequence at least 95% identical thereof, or any 19 contiguous nucleotides of SEQ ID NOs: 9, 12, or 14 or a sequence at least 95% identical thereof or any PaAos sequence in any guayule cultivar, or SEQ ID NO: 45), such that the dsRNA silences PaAos in the altered guayule which causes the altered guayule to produce more rubber than the amount of rubber produced by a non-altered guayule.

It is an object of this invention to have a method for increasing the amount of rubber produced by an altered guayule compared to the amount of rubber produced by a non-altered guayule. It is a further object that the method involves making one of the genetic alteration described supra in a non-altered guayule cell to produce a genetically altered guayule cell, such that the genetic alteration causes the genetically altered guayule to produce a reduced amount of functional PaAos compared the amount of functional PaAos produced by non-altered guayule cell and/or to produce an increased amount of one or more transcription factors (PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like) compared to the amount of the one or more transcription factors produced by a non-altered guayule; selecting for a genetically altered guayule cell that produces (i) a reduced amount of functional PaAos compared to the amount of functional PaAos produced by a non-altered guayule cell and/or (ii) an increased amount of PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like compared to the amount of PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like produced by a non-altered guayule; and growing the selected genetically altered guayule cell into a genetically altered guayule that produces more rubber than the non-altered guayule. It is a further object of this invention that the lower amount of functional PaAos produced and/or increased amount of PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like produced results in an increase in the amount of rubber produced by the genetically altered guayule compared to the amount of rubber produced by a non-altered guayule. It is another object of this invention that the genetically altered guayule is exposed to a temperature between approximately 7° C. and approximately 15° C. for approximately 8 hours per day and/or exposed to salicylic acid and/or exposed to PaAos dsRNA which results in a synergistic increase in the amount of rubber produced by the genetically altered guayule. Another object of this invention is to have a genetically altered guayule made using these methods and the progeny thereof. It is a further object of this invention to have germplasm, pollen, flowers, seeds, stems, leaves, roots, cells, etc., of these genetically altered guayule.

It is an object of this invention to have a method for increasing the amount of rubber produced by an altered guayule compared to the amount of rubber produced by a non-altered guayule. It is another object of this invention that the alteration induces RNAi to silence PaAos expression which is generated by transforming a non-altered guayule cell with an expression vector containing a heterologous promoter operably linked to a polynucleotide encoding PaAos anti-sense RNA. The polynucleotide can also encode a sequence complementary to PaAos anti-sense RNA sequence so that dsRNA is formed.

It is a further object of this invention to have a method for increasing the amount of rubber produced by an altered guayule compared to the amount of rubber produced by a non-altered guayule by administering salicylic acid (SA) and/or a PaAos dsRNA solution to a non-altered guayule to produce an altered guayule. The SA and/or PaAos dsRNA enter the altered guayule and cause the altered guayule to produce an increased amount of rubber compared to the amount of rubber produced by the non-altered guayule. It is another object of this invention that the PaAos dsRNA has a sequence of at least 19 contiguous nucleotides of the sequence of PaAos, at least 19 contiguous nucleotides of the reverse complementary sequence of PaAos, SEQ ID NO: 11 (or a sequence at least 95% identical thereof), and/or at least 19 contiguous nucleotides of SEQ ID NO: 11; or SEQ ID NO: 45. It is another object of this invention that an SA solution can have a concentration between approximately 0.1 nM to approximately 100 nM of SA. It is another object of this invention that the SA and/or PaAos dsRNA solution is administered to the plant by (i) spraying onto the plant, (ii) applying to soil surrounding the plant, (iii) applying to a root of plant and/or (iv) applying to irrigation water which is applied to soil surrounding the plant. It is another object of this invention that one can optionally expose the altered guayule to a temperature between approximately 7° C. and approximately 15° C. for approximately 8 hours per day which results in a synergistic increase in the amount of rubber produced by the altered guayule compared to a non-altered guayule exposed to the same temperatures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows the design of the plasmids used in Example 1 for the overexpression of PaAos (pND6-Aos), silencing of PaAos (pND6-AosiL), and for the control plasmid (pND6). Each expression vector features the NPTII gene to confer kanamycin resistance for selection, and the control plasmid contains the GUS (β-glucuronidase) reporter gene instead of PaAos or a portion of PaAos in reverse complementary orientation. Thus, one can use a histochemical GUS staining assay (the chromogenic substrate X-Gluc (C₁₄H₁₃BrCINO₇)) as a visual indicator of transformed tissues with the negative control plasmid.

FIG. 2 shows the primers used in the qRT-PCR, PCR reaction conditions, and the expected amplicon product size to determine RNA expression in the genetically altered guayule Amplicon (mRNA product) PaAos_(OE) is derived from plants transformed with pND6-Aos (Aos overexpression). Amplicon (mRNA product) PaAos_(RNAi) is derived from plants transformed with pND6-AosiL (Aos silencing). Amplicon (mRNA product) 18S is from 18S ribosome RNA. Amplicon (mRNA product) PaAos is for wild-type guayule plants with intact PaAos gene.

FIG. 3 provides size and weight measurements of the four types of guayule plants grown under different conditions in growth chambers. Plants are initially transferred to soil from tissue culture media and grown under greenhouse conditions for one month. Following, plants are moved to controlled-temperature growth chamber conditions under 27° C. (16 h)/25° C. (8 h) and at 27° C. (16 h)/10° C. (8 h). The four type of guayule plants are wild-type (G7-11.1 and G7-11.2), guayule transformed with the empty expression vector pND6 (pND6-10, pND6-12, pND6-35), guayule transformed with pND6-AosiL for silencing PaAos via RNAi (pND6-AosiL₇₋₂, pND6-AosiL₈₋₁, pND6-AosiL₉₋₁₆, pND6-AosiL₁₂₋₁,), and guayule transformed with pND6-Aos to overexpress PaAos (pND6-Aos₄₋₁, pND6-Aos₄₋₂, pND6-Aos₅₋₁, pND6-Aos₇₋₁,) at 2 months old. G7-11 is a breeder's nomenclature for what later became the USDA publicly released guayule Germplasm line AZ-2 (Reg. No. GP-9; PI 599676). The biomass of the shoot (leaves plus stems) and root are weighed in 2 months old guayule plants grown in growth chambers under 27° C. (16 h)/25° C. (8 h) and at 27° C. (16 h)/10° C. (8 h). The asterisks, (*), (**) and (***), indicate significant difference in comparison to (non-altered) G7-11 at p >0.05, 0.005 and 0.0005, respectively.

FIG. 4 shows SPAD values indicating leaf chlorophyll concentration (“SPAD units”) for wild-type guayule (G7-11), guayule transformed with the empty expression vector (pND6); guayule transformed with pND6-Aos (Oe), and guayule transformed with pND6-AosiL (RNAi) grown at 27° C. (16 h)/25° C. (8 h) or 27° C. (16 h)/10° C. (8 h).

FIG. 5 shows the number of branches and stem diameter of 2 months old genetically altered guayule (pND6-AosiL and pND6-Aos lines), non-altered guayule (G7-11) and empty vector control guayule (pND6) plants grown in growth chambers at 27° C. (16 h)/25° C. (8 h) or at 27° C. (16 h)/10° C. (8 h). pND6-AosiL genotypes have larger number of stems than the non-altered and empty vector controls. Additionally, the mature stembark tissues in pND6-AosiL have significantly thicker diameter (ranging from 35% to 54%) under both 27° C. (16 h)/25° C. (8 h) and 27° C. (16 h)/10° C. (8 h).

FIG. 6 shows results from gel permeation chromatography for elution of cyclohexane extractables from transformed and non-altered guayule plant lines. The natural rubber molecular weight is calculated using Astra software for three pND6-AosiL transformed guayule plants, three pND6-Aos transformed guayule plants, two pND6 transformed guayule plants, and non-altered guayule G7-11. The error bars represent 3 different plants with 3 technical replicates.

FIG. 7 shows the rubber content of SA (0 nM, 10 nM, and 100 nM) treated guayule G7-11 plants.

FIG. 8 shows PaAOS relative expression and rubber content analyzed by ASE in one month old soil-grown guayule G7-11 plants treated with salicylic acid for 2 months and grown in greenhouse settings.

FIG. 9A, FIG. 9B, and FIG. 9C show single nucleotide polymorphisms (SNP) in PaAos coding sequence for guayule cultivars W6 549 (“W6549”; SEQ ID NO: 12), G7-11 (SEQ ID NO: 9), and PI 478652 (“478652”; SEQ ID NO: 14). The SNPs are contained in boxes.

FIG. 10 shows an alignment of PaAos amino acid sequences obtained from guayule cultivars W6 549 (“W6549”; SEQ ID NO: 13), PI 478652 (“478652”; SEQ ID NO: 15) and G7-11 (SEQ ID NO: 10). The boxes highlight the different amino acids against the cultivars.

FIG. 11A, FIG. 11B, and FIG. 11C provide PaAos promoter's sequence (SEQ ID NO: 26) and indicates sequences that are putative binding sites of the indicated transcription factors.

FIG. 12 provides the names and sequences of various primers, their annealing temperatures and amplicon size.

FIGS. 13A-13C show the relative expression of WRKY3-like (FIG. 13A), WRKY71-like (FIG. 13B), and MYBS3-like (FIG. 13C) in non-altered guayule, genetically altered guayule with PaAos silenced, and genetically altered guayule with PaAos overexpressed.

DETAILED DESCRIPTION OF THE INVENTION

This invention involves a novel and unexpected method of increasing natural rubber yield in guayule plants by manipulating the expression of PaAos and/or reducing the amount of functional PaAos and/or reducing PaAos' functionality present in guayule. By altering the expression of PaAos and/or reducing the amount of functional PaAos and/or reducing PaAos' functionality, one also reduces the amount of functional PaAos in rubber particles. The rubber yield per acre is increased because the genetically altered guayule is also larger than non-altered guayule and has more tissue in which to store rubber. Genetically altered guayule that express the reverse complement of PaAos have reduced amounts of PaAos in the rubber particles via RNAi. Because these genetically altered guayule plants produce less PaAos, they also have altered amounts of various hormones that are produced in the biosynthetic pathway for which PaAos is one enzyme. In particular, the amount of jasmonic acid, abscisic acid, gibberellin A₂₀, gibberellin A₁, and gibberellin A₃ are decreased in the RNAi genetically altered guayule while the amount of salicylic acid (SA) is increased, compared to non-genetically altered guayule. Using RNAi technology to reduce the amount of PaAos in the plant, these genetically altered guayule unexpectedly and surprisingly have increased amount of rubber compared to non-altered guayule plants AND more biomass which increases the rubber yield. One optionally exposes the genetically altered guayule to cold temperature (between approximately 7° C. and approximately 15° C. or between approximately 10° C. and approximately 15° C.; approximately 8 hours per day) which, surprisingly and unexpectedly, acts synergistically with the reduced PaAos transcription (and/or reduced amount of functional PaAos) to increase the amount of rubber production even greater than to the amount produced by non-altered guayule. Methods of enhancing rubber yield via suppression of PaAos expression via RNAi and similar technologies, and markers for the identification of such guayule with altered PaAos are provided. For the purposes of this invention, the terms “function”, “functional”, and “functionality” include any activity that the protein or other compound possesses. A protein/compound may have enzymatic activity, binding activity, transporting activity, structural activity, etc.

As mentioned above, one embodiment of this invention involves using RNAi to reduce production of PaAos which causes an increase in rubber production and biomass of the genetically altered guayule. In another embodiment, the invention involves altering the genomic PaAos sequence such that no functional PaAos is produced (a “null” mutation), or that the encoded protein has reduced functionality compared to the activity of non-modified PaAos. When no functional PaAos is produced or when PaAos with reduced functionality is produced, then it is understood that the altered guayule produces “a reduced amount of functional PaAos”. Such altered guayule producing a reduced amount of functional PaAos is another embodiment of this invention. In yet another embodiment, the invention involves increasing the amount of SA in guayule which results in increased amount of rubber being produced compared to the amount of rubber produced in guayule which does not have increased amount of SA. One embodiment involves administering an effective amount of SA to a non-altered guayule, which causes the treated guayule to reduce PaAos expression and/or reduce the amount of functional PaAos, and thus increases the amount of rubber produced by the treated guayule compared to the amount of rubber produced by a non-altered guayule.

Another embodiment of this invention involves an altered guayule producing more rubber than the amount of rubber produced by a non-altered guayule. In one embodiment, the altered guayule overexpresses one or more transcription factors (PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like) using an expression vector that contains a heterologous promoter operably linked to the coding sequences of one or more of these transcription factors (SEQ ID NOs: 39 and 40, 41 and 42, and/or 43 and 44, or a sequence at least 95% identical thereof for PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like, respectively). In another embodiment, the altered guayule contains an expression vector that produces PaAos dsRNA or anti-sense RNA so that less amount of PaAos is produced by the altered guayule. In another embodiment, the altered guayule contains a mutated PaAos and the altered guayule produces PaAos with reduced or no functionality, compared to the functionality of PaAos in a non-altered guayule. In yet another embodiment, any of these genetic alterations are present in the guayule. In yet another embodiment, one optionally subjects any of the altered guayule to cold temperatures and/or administers SA to the altered guayule and/or administers dsRNA for PaAos to the altered guayule to increase rubber production in the altered guayule compared to the amount of rubber produced by a non-altered guayule.

Because this invention involves production of genetically altered plants and involves recombinant DNA techniques, the following definitions are provided to assist in describing this invention. The terms “isolated”, “purified”, or “biologically pure” as used herein, refer to material that is substantially or essentially free from components that normally accompany the material in its native state or when the material is produced. In an exemplary embodiment, purity and homogeneity are determined using analytical chemistry techniques such as polyacrylamide gel electrophoresis or high performance liquid chromatography. A nucleic acid or particular bacteria that are the predominant species present in a preparation is substantially purified. In an exemplary embodiment, the term “purified” denotes that a nucleic acid or protein that gives rise to essentially one band in an electrophoretic gel. Typically, isolated nucleic acids or proteins have a level of purity expressed as a range. The lower end of the range of purity for the component is about 60%, about 70% or about 80% and the upper end of the range of purity is about 70%, about 80%, about 90% or more than about 90%.

The term “gene” refers to a DNA sequence involved in producing a RNA or polypeptide or precursor thereof. The polypeptide or RNA is encoded by a full-length coding sequence (cds) or by intron-interrupted portions of the coding sequence, such as exon sequences. In one embodiment of this invention, the gene involved is Parthenium argentatum allene oxide synthase (PaAos or Aos). PaAos cDNA and amino acid sequence is found in GenBank accession number X78166.2 which is cultivar G7-11 (wild-type/non-altered) (USDA publicly released guayule Germplasm line AZ-2 (Reg. No. GP-9; PI 599676)). The cDNA sequence is in SEQ ID NO: 9; the protein sequence is in SEQ ID NO: 10. SEQ ID NO: 12 is the cDNA sequence for PaAos and SEQ ID NO: 13 is the amino acid sequence for PaAos in guayule W6549 cultivar. SEQ ID NO: 14 is the cDNA sequence for PaAos and SEQ ID NO: 15 is the amino acid sequence for PaAos in guayule 478652 cultivar. In one embodiment, the reverse complementary sequence of PaAos (negative strand) (or a sequence that is at least 95% identical) is operably linked to a heterologous promoter to produce RNA have a complementary sequence to the mRNA made from PaAos (SEQ ID NOs: 9, 12, or 14 or the sequence present any other cultivar) (positive strand). In one embodiment, one uses the sequence in SEQ ID NO: 11 (or a sequence that is at least 95% identical) as a portion of the reverse complement polynucleotide of PaAos, or use SEQ ID NO: 45. In another embodiment, DNA encoding one or more of the transcription factors PaWRKY3-like (SEQ ID NOs: 39 and 40 or a sequence at least 95% identical thereof), PaWRKY71-like (SEQ ID NOs: 41 and 42 or a sequence at least 95% identical thereof), and PaMYBS3-like (SEQ ID NOs: 43 and 43 or a sequence at least 95% identical thereof) are overexpressed in an altered guayule.

The term “nucleic acid” as used herein, refers to a polymer of ribonucleotides or deoxyribonucleotides. Typically, “nucleic acid” polymers occur in either single- or double-stranded form, but are also known to form structures comprising three or more strands. The term “nucleic acid” includes naturally occurring nucleic acid polymers as well as nucleic acids comprising known nucleotide analogs or modified backbone residues or linkages, which are synthetic, naturally occurring, and non-naturally occurring, which have similar binding properties as the reference nucleic acid, and which are metabolized in a manner similar to the reference nucleotides. Exemplary analogs include, without limitation, phosphorothioates, phosphoramidates, methyl phosphonates, chiral-methyl phosphonates, 2-O-methyl ribonucleotides, peptide-nucleic acids (PNAs). “DNA”, “RNA”, “polynucleotides”, “polynucleotide sequence”, “oligonucleotide”, “nucleotide”, “nucleic acid”, “nucleic acid molecule”, “nucleic acid sequence”, “nucleic acid fragment”, and “isolated nucleic acid fragment” are used interchangeably herein.

For nucleic acids, sizes are given in either kilobases (kb) or base pairs (bp), or nucleotides (nt). Estimates are typically derived from agarose or acrylamide gel electrophoresis, from sequenced nucleic acids, or from published DNA sequences. For proteins, sizes are given in kiloDaltons (kDa) or amino acid residue numbers. Proteins sizes are estimated from gel electrophoresis, from sequenced proteins, from derived amino acid sequences, or from published protein sequences.

Unless otherwise indicated, a particular nucleic acid sequence for each amino acid substitution (alteration) also implicitly encompasses conservatively modified variants thereof (e.g., degenerate codon substitutions), the complementary (or complement) sequence, and the reverse complement sequence, as well as the sequence explicitly indicated. Specifically, degenerate codon substitutions may be achieved by generating sequences in which the third position of one or more selected (or all) codons is substituted with mixed-base and/or deoxyinosine residues (see e.g., Batzer et al., Nucleic Acid Res. 19:5081 (1991); Ohtsuka et al., J. Biol. Chem. 260:2605-2608 (1985); and Rossolini et al., Mol. Cell. Probes 8:91-98(1994)). Because of the degeneracy of nucleic acid codons, one can use various different polynucleotides to encode identical polypeptides. Table 1, infra, contains information about which nucleic acid codons encode which amino acids and is useful for determining the possible nucleotide substitutions that are included in this invention.

TABLE 1 Amino acid Nucleic acid codons Amino acid Nucleic acid codons Ala/A GCT, GCC, GCA, GCG Leu/L TTA, TTG, CTT, CTC, CTA, CTG Arg/R CGT, CGC, CGA, CGG, AGA, AGG Lys/K AAA, AAG Asn/N AAT, AAC Met/M ATG Asp/D GAT, GAC Phe/F TTT, TTC Cys/C TGT, TGC Pro/P CCT, CCC, CCA, CCG Gln/Q CAA, CAG Ser/S TCT, TCC, TCA, TCG, AGT, AGC Glu/E GAA, GAG Thr/T ACT, ACC, ACA, ACG Gly/G GGT, GGC, GGA, GGG Trp/W TGG His/H CAT, CAC Tyr/Y TAT, TAC Ile/I ATT, ATC, ATA Val/V GTT, GTC, GTA, GTG Stop TAA, TGA, TAG

In addition to the degenerate nature of the nucleotide codons which encode amino acids, alterations in a polynucleotide that result in the production of a chemically equivalent amino acid at a given site, but do not affect the functional properties of the encoded polypeptide, are well known in the art. “Conservative amino acid substitutions” are those substitutions that are predicted to interfere least with the properties of the reference polypeptide. In other words, conservative amino acid substitutions substantially conserve the structure and the function of the reference protein. Thus, a codon for the amino acid alanine, a hydrophobic amino acid, may be substituted by a codon encoding another less hydrophobic residue, such as glycine, or a more hydrophobic residue, such as valine, leucine, or isoleucine. Similarly, changes which result in substitution of one negatively charged residue for another, such as aspartic acid for glutamic acid, or one positively charged residue for another, such as lysine for arginine or histidine, is also expected to produce a functionally equivalent protein or polypeptide. Table 2 provides a list of exemplary conservative amino acid substitutions. Conservative amino acid substitutions generally maintain (a) the structure of the polypeptide backbone in the area of the substitution, for example, as a beta sheet or alpha helical conformation, (b) the charge or hydrophobicity of the molecule at the site of the substitution, and/or (c) the bulk of the side chain. In another embodiment, groups of amino acids that are conservative substitutions for each other are (i) alanine (Ala or A), serine (Ser or S), and threonine (Thr or T); (ii) aspartic acid (Asp or D) and glutamic acid (Glu or E); (iii) asparagine (Asn or N) and glutamine (Gln or Q); (iv) arginine (Arg or R) and lysine (Lys or K); (v) isoleucine (Ile or I), leucine (Leu or L), methionine (Met or M), and valine (Val or V); and (vi) phenylalanine (Phe or F), tyrosine (Tyr or Y), and tryptophan (Trp or W). See, Creighton, Proteins, W.H. Freeman and Co. (1984), contents of which are expressly incorporated herein. In yet another embodiment, amino acid(s) that are conservative substitutes for one amino acid are grouped by the following characteristics: aliphatic amino acids (alanine, glycine, isoleucine, leucine, and valine); hydroxyl or sulfur containing amino acids (cysteine, serine, methionine, and threonine); cyclic (proline); aromatic (phenylalanine, tryptophan, and tyrosine); basic (arginine, histidine, and lysine); acidic (aspartate and glutamate); and uncharged (asparagine and glutamine).

TABLE 2 Amino Acid Conservative Substitute Ala Gly, Ser Arg His, Lys Asn Asp, Gln, His Asp Asn, Glu Cys Ala, Ser Gln Asn, Glu, His Glu Asp, Gln, His Gly Ala His Asn, Arg, Gln, Glu Ile Leu, Val Leu Ile, Val Lys Arg, Gln, Glu Met Ile, Leu Phe His, Leu, Met, Trp, Tyr Ser Cys, Thr Thr Ser, Val Trp Phe, Tyr Tyr His, Phe, Trp Val Ile, Leu, Thr

The term “primer” refers to an oligonucleotide which may act as a point of initiation of DNA extension. A primer may occur naturally, as in a purified restriction digest, or may be produced synthetically.

A primer is selected to be “substantially complementary” to a strand of specific sequence of the template. A primer must be sufficiently complementary to hybridize with a template strand for primer elongation to occur. A primer sequence need not reflect the exact sequence of the template. For example, a non-complementary nucleotide fragment may be attached to the 5′ end of the primer, with the remainder of the primer sequence being substantially complementary to the strand. Non-complementary bases or longer sequences can be interspersed into the primer, provided that the primer sequence is sufficiently complementary with the sequence of the template to hybridize and thereby form a template primer complex for synthesis of the extension product of the primer.

“dsRNA” refers to double-stranded RNA that contains a sense region and an antisense region of a selected target gene (or sequences with high sequence identity thereto so that gene silencing occurs), as well as any smaller double-stranded RNAs formed therefrom by RNAse or Dicer activity. Such dsRNA may include portions of single-stranded RNA, but contains at least 18 base pairs of dsRNA. A dsRNA after been processed by Dicer generates siRNAs (18-25 bp in length) that are double-strand, and could contain ends with 2 nucleotide overhangs, which will be single-stranded. It is predicted that usually siRNA around 19 nt in length (or, alternatively, between 17 and 27 nt in length), will be incorporated into RISC. In one embodiment, the sense region and the antisense region of a dsRNA are on the same strand of RNA and are separated by a linker. In this embodiment, when the sense region and the antisense region anneal together, the dsRNA contains a loop which is the linker. One promoter operably linked to the DNA or RNA encoding both the sense region and the antisense region is used to produce the one RNA molecule containing both the sense region and the anti-sense region. In another embodiment, the sense region and the antisense region are present on two distinct strands of RNA (a sense strand and the anti-sense strand which is complementary to the sense strand) which anneal together to form the dsRNA. In this embodiment, a promoter is operably linked to each strand of DNA or RNA; where one DNA or RNA strand encodes the RNA containing the sense region and the other strand of DNA or RNA encodes the RNA containing the anti-sense region. In this embodiment, the promoter on each strand may be the same as or different from the promoter on the other strand. After the RNAs are transcribed, two RNA strands anneal together because the sense region and the anti-sense region are complementary to each other, thus forming the dsRNA. In yet another embodiment, one strand of DNA or RNA can encode both the sense region and the anti-sense region of the dsRNA. However, the DNA or RNA coding each region are separated from each other so that two promoters are necessary to transcribe each region. That is, the DNA or RNA encoding the anti-sense region and the DNA or RNA encoding the sense region are operably linked to their own promoter. Again, the two promoters may be the same promoter or different promoters. In one embodiment, the promoter can be a T7 RNA polymerase promoter. Other promoters are well-known in the art and can be used (see discussion infra). While many embodiments of this invention use DNA to encode the sense region and/or anti-sense region, as described infra, it is possible to use a recombinant RNA virus to produce the dsRNA described herein. In such cases, a virus has had its genome altered so that the infected cell produces one of the sequences of PaAos described herein or the reverse complement thereof or both.

Active dsRNA molecules have worked when they were as long as 1,000 bp, and should work when even longer. For the purposes of the inventions described herein, any siRNA having at least 19 nt length derived fromPaAos, or the reverse complement sequence thereof and that are specific to PaAos. In one embodiment, the dsRNA may be any 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 45, 50, 55, 60, or longer contiguous nucleotides, up and including the full-length of PaAos cDNA (SEQ ID NOs: 9, 12, and/or 14 or a sequence at least 95% identity thereof or the sequence of any other PaAos). In another embodiment, the reverse complement sequence of PaAos is SEQ ID NO: 11 or a sequence at least 95% identity thereof, or SEQ ID NO: 45. In alternative embodiments, the dsRNA ranges in length between 16 bp and 30 bp, between 16 bp and 25 bp, between 18 and 30 bp, and between 19 bp and 28 bp. In yet another embodiment, RNA forms that are created by RNAse III family (Dicer or Dicer-like ribonuclease) or Dicer activity that are longer dsRNA are within the scope of this invention.

One uses computer programs to predict dsRNA sequences that will be effective in reducing production of the desired gene/protein (in this embodiment PaAos and PaAos). Information about such computer programs are be found on the following two websites: genelink com/siRNA/RNAiwhatis.asp; and rnaiweb.com/RNAi/RNAi_Web_Resources/RNAi_Tools_Software/Online_siRNA_Design_Tools/inde x.html. Using such computer programs, one can obtain sequences that differ from SEQ ID NO: 11 which can be used to generate dsRNA via binding to PaAos mRNA. Alternatively, one can determine an appropriate sequence to test using the methodologies described in Preuss, S. and Pikaard, C. S. (2003) Targeted gene silencing in plants using RNA interference, in RNA interference (RNAi)-Nuts and Bolts of siRNA Technology (Engelke, D., Ed.), pp 23-36, DNA Press, LLC.

siRNA may be synthetically made, expressed and secreted directly from a transformed cell, or microbe, or generated from a longer dsRNA by enzymatic activity. These siRNAs may be blunt-ended or have 1 bp to 4 bp overlapping ends of various nucleotide combinations. Also modified microRNAs comprising a portion of PaAos and its reverse complementary sequence are included herein as dsRNAs. In one embodiment of the invention, the dsRNA is expressed in a plant to be protected, or expressed in microorganisms which can be endemic organisms of the plant (microbes, virus, phytoplasma, viroids, fungal, protists) or free-living microbes (yeasts, bacteria, protists, fungi) any of which are delivered, alive, dead or processed, via root treatments, or foliar sprayed on plants, or injected into plants, which are to be protected. Alternatively, the microorganism can be a transgenic organism endemic to the plant and deliver dsRNA to the plant. See, e.g., Subhas, et al. (2014) J. Biotech. 176:42-49 for an example of virus induced gene silencing using Citrus tristeza virus. See, also, Tenllado, et al. (2003) BMC Biotechnol 3:3 for an example of a crude extract of a bacterial cell culture containing dsRNA that protects plants against viral infections.

In one embodiment, a dsRNA solution is administered to the guayule plant. A dsRNA solution contains one or more of the dsRNAs discussed herein and an agriculturally acceptable carrier. An agriculturally acceptable carrier can be water, one or more liposomes, one or more lipids, one or more surfactants, one or more proteins, one or more peptides, one or more nanotubes, chitin, and/or one or more inactivated microorganisms that encapsulate the dsRNA. See WO 2003/004644 for examples of other agriculturally acceptable carriers, contents of which are expressly incorporated herein. The dsRNA solution may also contain one or more sugars, compounds that assist in preventing dsRNA degradation, translaminar chemicals, chemical brighteners, clays, minerals, and/or fertilizers. One can spray the dsRNA solution on plants (leaves, branches, trunk, exposed roots, etc.). One can apply the dsRNA solution to the soil around the plant so that the plant's roots absorb the dsRNA solution and transport it to other parts of the plants. Alternatively, one or more roots can be placed in a container which contains the dsRNA solution so that those roots absorb the dsRNA solution. The dsRNA solution can also be injected into the plant. As such, the dsRNA solution may be in a spray dsRNA solution, a drenching dsRNA solution, or an injectable dsRNA solution. The dsRNA may also be mixed into irrigation water which is then administered to the plants. The plant's roots will absorb the dsRNA in the irrigation water, resulting in RNAi. Other types of solutions are known in the art.

In another embodiment, one administers dsRNA and salicylic acid to a non-altered guayule or to a guayule with a genetic alteration (such as overexpressing one or more of the transcription factors PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like) to increase rubber production which would yield more rubber than the amount of rubber produced by a non-altered guayule, under the same conditions. The dsRNA and salicylic acid are administered concurrently or sequentially. They can be administered via irrigation water, by administering the dsRNA and/or salicylic acid to the soil around the plant, by placing a root of the plant into a container holding the dsRNA and/or salicylic acid, spraying the dsRNA and/or salicylic acid onto the plant, or a combination thereof. For example, the dsRNA could be sprayed onto the plant while the salicylic acid is added to the irrigation water and applied to the soil around the plant. Root drenching with dsRNA and/or salicylic acid is yet another embodiment. In yet another embodiment, one administers the dsRNA and salicylic acid to the plant prior to or when the temperature is cold (between approximately 7° C. and approximately 15° C. or between approximately 10° C. and approximately 15° C.; for approximately 8 hours per day). The treated guayule will produce more rubber than the amount of rubber produced by the untreated guayule.

Oligonucleotides and polynucleotides that are not commercially available can be chemically synthesized e.g., according to the solid phase phosphoramidite triester method first described by Beaucage and Caruthers, Tetrahedron Letts. 22:1859-1862 (1981), or using an automated synthesizer, as described in Van Devanter et al., Nucleic Acids Res. 12:6159-6168 (1984). Other methods for synthesizing oligonucleotides and polynucleotides are known in the art. Purification of oligonucleotides is by either native acrylamide gel electrophoresis or by anion-exchange HPLC as described in Pearson & Reanier, J. Chrom. 255:137-149 (1983).

The terms “identical” or percent “identity”, in the context of two or more polynucleotides or polypeptide sequences, refer to two or more sequences or sub-sequences that are the same or have a specified percentage of nucleotides or amino acids (respectively) that are the same (e.g., 80%, 85% identity, 90% identity, 99%, or 100% identity), when compared and aligned for maximum correspondence over a designated region as measured using a sequence comparison algorithm or by manual alignment and visual inspection.

The phrase “high percent identical” or “high percent identity”, in the context of two polynucleotides or polypeptides, refers to two or more sequences or sub-sequences that have at least about 80%, identity, at least about 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% nucleotide or amino acid identity, when compared and aligned for maximum correspondence, as measured using a sequence comparison algorithm or by visual inspection. In an exemplary embodiment, a high percent identity exists over a region of the sequences that is at least about 16 nucleotides or amino acids in length. In another exemplary embodiment, a high percent identity exists over a region of the sequences that is at least about 50 nucleotides or amino acids in length. In still another exemplary embodiment, a high percent identity exists over a region of the sequences that is at least about 100 nucleotides or amino acids or more in length. In one exemplary embodiment, the sequences are high percent identical over the entire length of the polynucleotide or polypeptide sequences.

For sequence comparison, typically one sequence acts as a reference sequence, to which test sequences are compared. When using a sequence comparison algorithm, test and reference sequences are entered into a computer, subsequence coordinates are designated, if necessary, and sequence algorithm program parameters are designated. Default program parameters may be used, or alternative parameters designated. The sequence comparison algorithm then calculates the percent sequence identities for the test sequences relative to the reference sequence, based on the program parameters. Methods of alignment of sequences for comparison are well-known in the art. Optimal alignment of sequences for comparison is conducted, e.g., by the local homology algorithm of Smith & Waterman, Adv. Appl. Math. 2:482 (1981), by the homology alignment algorithm of Needleman & Wunsch, J. Mol. Biol. 48:443 (1970), by the search for similarity method of Pearson & Lipman, Proc. Natl. Acad. Sci. USA 85:2444 (1988), by computerized implementations of various algorithms (GAP, BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package, Genetics Computer Group, 575 Science Dr., Madison, Wis.), and/or by manual alignment and visual inspection (see, e.g., Ausubel et al. (eds.), Current Protocols in Molecular Biology, 1995 supplement).

The “complement” of a particular polynucleotide sequence is that nucleotide sequence which would be capable of forming a double-stranded DNA or RNA molecule with the represented nucleotide sequence, and which is derived from the represented nucleotide sequence by replacing the nucleotides by their complementary nucleotide according to Chargaff's rules (A<>T; G<>C) and reading in the 5′ to 3′ direction, i.e., in opposite direction of the represented nucleotide sequence (reverse complement).

In one embodiment of the invention, sense and antisense RNAs and dsRNA can be separately expressed in-vitro or in-vivo. In-vivo production of sense and antisense RNAs may use different chimeric polynucleotide constructs using the same or different promoters or using an expression vector containing two convergent promoters in opposite orientation. The sense and antisense RNAs which are formed (e.g., in the same host cells or synthesized) then combine to form dsRNA. To be clear, whenever reference is made herein to a dsRNA chimeric or fusion polynucleotide or a dsRNA molecule, that such dsRNA formed (e.g., in plant cells) from sense and antisense RNA produced separately is also included. Also, synthetically made dsRNA and self-annealing RNA strands are included herein when the sense and antisense strands are present together.

As used herein, the term “promoter” refers to a polynucleotide that, in its native state, is located upstream or 5′ to a translational start codon of an open reading frame (or protein-coding region) and that is involved in recognition and binding of RNA polymerase and other proteins (trans-acting transcription factors) to initiate transcription. A “plant promoter” is a native or non-native promoter that is functional in plant cells, even if the promoter is present in a microorganism that infects plants or a microorganism that does not infect plants. The promoters that are predominately functional in a specific tissue or set of tissues are considered “tissue-specific promoters”. A plant promoter can be used as a 5′ regulatory element for modulating expression of a particularly desired polynucleotide (heterologous polynucleotide) operably linked thereto. When operably linked to a transcribable polynucleotide, a promoter typically causes the transcribable polynucleotide to be transcribed in a manner that is similar to that of which the promoter is normally associated.

Plant promoters include promoters produced through the manipulation of known promoters to produce artificial, chimeric, or hybrid promoters. Such promoters can also combine cis-elements from one or more promoters, for example, by adding a heterologous regulatory element to an active promoter with its own partial or complete regulatory elements. The term “cis-element” refers to a cis-acting transcriptional regulatory element that confers an aspect of the overall control of gene expression. A cis-element may function to bind transcription factors, trans-acting protein factors that regulate transcription. Some cis-elements bind more than one transcription factor, and transcription factors may interact with different affinities with more than one cis-element.

The term “vector” refers to DNA, RNA, a protein, or polypeptide that are to be introduced into a host cell or organism. The polynucleotides, protein, and polypeptide which are to be introduced into a host may be therapeutic or prophylactic in nature; may encode or be an antigen; may be regulatory in nature; etc. There are various types of vectors including viruses, viroids, plasmids, bacteriophages, cosmids, and bacteria.

An expression vector is nucleic acid capable of replicating in a selected host cell or organism. An expression vector can replicate as an autonomous structure, or alternatively integrate, in whole or in part, into the host cell chromosomes or the nucleic acids of an organelle, or it is used as a shuttle for delivering foreign DNA to cells, and thus replicate along with the host cell genome. Thus, an expression vector are polynucleotides capable of replicating in a selected host cell, organelle, or organism, e.g., a plasmid, virus, artificial chromosome, nucleic acid fragment, and for which certain genes on the expression vector (including genes of interest) are transcribed and translated into a polypeptide or protein within the cell, organelle or organism; or any suitable construct known in the art, which comprises an “expression cassette”. In contrast, as described in the examples herein, a “cassette” is a polynucleotide containing a section of an expression vector. The use of the cassettes assists in the assembly of the expression vectors. An expression vector is a replicon, such as plasmid, phage, virus, chimeric virus, or cosmid, and which contains the desired polynucleotide sequence operably linked to the expression control sequence(s).

A heterologous polynucleotide sequence is operably linked to one or more transcription regulatory elements (e.g., promoter, terminator and, optionally, enhancer) such that the transcription regulatory elements control and regulate the transcription and/or translation of that heterologous polynucleotide sequence. A cassette has the heterologous polynucleotide operably linked to one or more transcription regulatory elements. As used herein, the term “operably linked” refers to a first polynucleotide, such as a promoter, connected with a second transcribable polynucleotide, such as a gene of interest, where the polynucleotides are arranged such that the first polynucleotide affects the transcription of the second polynucleotide. In some embodiments, the two polynucleotide molecules are part of a single contiguous polynucleotide. In other embodiments, the two polynucleotides are adjacent. For example, a promoter is operably linked to a gene of interest if the promoter regulates or mediates transcription of the gene of interest in a cell. Similarly, a terminator is operably linked to the polynucleotide of interest if the terminator regulates or mediates transcription of the polynucleotide of interest, and, in particular, the termination of transcription. Constructs of the present invention would typically contain a promoter operably linked to a transcribable polynucleotide operably linked to a terminator.

The term “recombinant” when used with reference, e.g., to a cell, or nucleic acid, protein, or vector, indicates that the cell, organism, nucleic acid, protein or vector, has been altered by the introduction of a heterologous nucleic acid or protein or the alteration of a native nucleic acid or protein, or that the cell is derived from a cell so altered. Thus, for example, recombinant cells may express genes/polynucleotides that are not found within the native (non-recombinant or non-altered or wild-type) form of the cell or express native genes in an otherwise abnormal amount—over-expressed, under-expressed or not expressed at all—compared to the non-altered cell or organism. In particular, one alters the genomic DNA of a non-altered plant by molecular biology techniques that are well-known to one of ordinary skill in the art and generate a recombinant plant.

The terms “transgenic”, “transformed”, “transformation”, and “transfection” are similar in meaning to “recombinant”. “Transformation”, “transgenic”, and “transfection” refer to the transfer of a polynucleotide into a host organism or into a cell. Such a transfer of polynucleotides may result in genetically stable inheritance of the polynucleotides or in the polynucleotides remaining extra-chromosomally (not integrated into the chromosome of the cell). Genetically stable inheritance may potentially require the transgenic organism or cell to be subjected for a period of time to one or more conditions which require the transcription of some or all of the transferred polynucleotide in order for the transgenic organism or cell to live and/or grow. Polynucleotides that are transformed into a cell but are not integrated into the host's chromosome remain as an expression vector within the cell. One may need to grow the cell under certain growth or environmental conditions in order for the expression vector to remain in the cell or the cell's progeny. Further, for expression to occur the organism or cell may need to be kept under certain conditions. Genetically altered organisms or cells containing the recombinant polynucleotide are referred to as “transgenic” or “transformed” organisms or cells or simply as “transformants”, as well as recombinant organisms or cells.

A genetically altered organism is any organism with any changes to its genetic material involving the invention described herein, whether in the nucleus or cytoplasm (organelle). As such, a genetically altered organism may be a recombinant or transformed organism. A genetically altered organism may also be an organism that was subjected to one or more mutagens or the progeny of an organism that was subjected to one or more mutagens and has mutations in its DNA caused by the one or more mutagens, as compared to the wild-type organism (i.e., organism not subjected to the mutagens) or the non-altered organism (i.e., one that contains alterations that are not the subject matter of this invention). Also, an organism that has been bred to incorporate a mutation into its genetic material is a genetically altered organism.

The term “altered” means that a change occurred compared to the “non-altered” item. However, a “non-altered” item could contain changes that are induced by man, but those changes are not the subject matter of the inventions described herein. For example, a non-altered guayule contains none of the described genetic changes nor has been treated with any of the described external substance, but may contain pre-existing changes which are not part of this invention. An altered guayule (which also is a genetically altered guayule) may contain a non-native expression vector that produces dsRNA or anti-sense RNA involving PaAOS or another gene and/or produces one or more transcription factors described herein or another gene. An altered guayule is also one which has been treated with a substance, such as dsRNA or salicylic acid (SA). An altered guayule may also have both types of changes.

Transformation and generation of genetically altered monocotyledonous and dicotyledonous plant cells is well known in the art. See, e.g., Weising, et al., Ann. Rev. Genet. 22:421-477 (1988); U.S. Pat. No. 5,679,558; Agrobacterium Protocols, ed: Gartland, Humana Press Inc. (1995); and Wang, et al. Acta Hort. 461:401-408 (1998). A method to generate genetically altered guayule is described in U.S. Pat. No. 9,018,449 (Dong & Cornish) and in Dong, et al., Plant Cell Reports 25:26-34 (2006). A method to generate transplastomic guayule is provided in U.S. Patent Application Publication 2014/0325699, the contents of which are expressly incorporated herein. The choice of method varies with the type of plant to be transformed, the particular application, and/or the desired result. The appropriate transformation technique is readily chosen by the skilled practitioner.

A polynucleotide encoding PaAos (SEQ ID NOs: 9, 12 and/or 14), the reverse complement of PaAos, or a portion thereof (e.g., SEQ ID NO: 11), operably linked to one or two appropriate promoters, can be stably inserted in a conventional manner into the genome (cytoplasmic genome or nucleic genome) of a single plant cell, and the altered plant cell can be used in a conventional manner to produce a genetically altered plant that produces the dsRNA of this invention. In this regard, a disarmed Ti-plasmid, containing the polynucleotide of this invention, in Agrobacterium tumefaciens can be used to genetically alter the plant cell, and thereafter, a genetically altered plant can be regenerated from the genetically altered plant cell using the procedures described in the art, for example, in EP 0 116 718, EP 0 270 822, WO 84/02913 and EP 0 242 246. Plant regeneration from cultured protoplasts is described in Evans et al., Protoplasts Isolation and Culture, in Handbook of Plant Cell Culture, pp. 124-176, MacMillan Publishing Company, New York, 1983; and Binding, Regeneration of Plants, in Plant Protoplasts, pp. 21-73, CRC Press, Boca Raton, 1985. Regeneration can also be obtained from plant callus, explants, organs, or parts thereof. Such regeneration techniques are described generally in Klee, et al., Ann. Rev. of Plant Phys. 38:467-486 (1987). Similarly, a polynucleotide encoding PaWRKY3-like, PaWRKY71-like, and/or PaMYBS3-like (the genomic sequence or coding sequence) may be incorporated into altered guayule.

Preferred Ti-plasmid vectors each contain the polynucleotides described herein between the border sequences, or at least located to the left of the right border sequence, of the T-DNA of the Ti-plasmid. Of course, other types of vectors may be used to transform the plant cell, using procedures such as direct gene transfer (as described, for example in EP 0 233 247), pollen mediated transformation (as described, for example in EP 0 270 356, WO 85/01856, and U.S. Pat. No. 4,684,611), plant RNA virus-mediated transformation (as described, for example in EP 0 067 553 and U.S. Pat. No. 4,407,956), liposome-mediated transformation (as described, for example in U.S. Pat. No. 4,536,475), and other methods such as the methods for transforming certain lines of corn (e.g., U.S. Pat. No. 6,140,553; Fromm, et al., Bio/Technology 8:833-839 (1990); Gordon-Kamm, et al., The Plant Cell 2:603-618 (1990) and rice (Shimamoto, et al., Nature 338:274-276 (1989); Datta et al., Bio/Technology 8:736-740 (1990)) and the method for transforming monocots generally (WO 92/09696). For cotton transformation, the method described in WO 2000/71733 can be used. For soybean transformation, reference is made to methods known in the art, e.g., Hinchee, et al. (Bio/Technology 6:915 (1988)) and Christou, et al. (Trends Biotechnology 8:145 (1990)) or the method of WO 00/42207.

The resulting genetically altered plant can be used in a conventional plant breeding scheme to produce more genetically altered plants with the same characteristics or to introduce the polynucleotide into other varieties of the same or related plant species. Seeds, which are obtained from the genetically altered plants, contain the expression vector as a stable genomic insert. Altered plants include plants having or derived from root stocks of altered plants containing the expression vector. Hence, any non-altered grafted plant parts inserted on a genetically altered plant or plant part are included in the invention.

For a genetically altered plant that produces dsRNA, one constructs an expression vector or cassette (made from DNA) that encodes, at a minimum, a first promoter and the dsRNA sequence of interest such that the promoter sequence is 5′ (upstream) to and operably linked to the dsRNA sequence. The expression vector or cassette may optionally contain a second promoter (same as or different from the first promoter) upstream and operably linked to the reverse complementary sequence of the dsRNA sequence such that two strands of RNA that are complementary to each other are produced. Alternatively, the expression vector or cassette can contain one promoter operably linked to both the dsRNA sequence (sense strand) in question and the complement or reverse complement of the dsRNA sequence (anti-sense strand) in question, such that the transcribed RNA bends on itself and the two desires sequences anneal. Alternatively, a second expression vector or cassette (made from DNA) may encode, at a minimum, a second promoter (same as or different from the promoter) operably linked to the reverse complementary sequence of the dsRNA such that two strands of complementary RNA are produced in the plant. The expression vector(s) or cassette(s) is/are inserted in a plant cell genome (nuclear or cytoplasmic). The promoter(s) used should be a promoter(s) that is/are active in a plant and is/are heterologous to PaAos (not normally driving the transcription of RNA of genomic PaAos). Of course, the expression vector or cassette may have other transcription regulatory elements, such as enhancers, terminators, etc.

Promoters (and more specifically, heterologous promoters for PaAos, the reverse complement of PaAos, and the transcription factors) that are active in plants are well-known in the field. Such promoters may be constitutive, inducible, and/or tissue-specific. Non-limiting examples of constitutive plant promoters include 35S promoters of the cauliflower mosaic virus (CaMV) (e.g., of isolates CM 1841 (Gardner, et al., Nucleic Acids Research 9:2871-2887 (1981)), CabbB-S (Franck, et al., Cell 21:285-294 (1980)) and CabbB-JI (Hull and Howell, Virology 86:482-493 (1987))), ubiquitin promoter (e.g., the maize ubiquitin promoter of Christensen, et al., Plant Mol. Biol. 18:675-689 (1992)), gos2 promoter (de Pater, et al., The Plant J. 2:834-844 (1992)), emu promoter (Last, et al., Theor. Appl. Genet. 81:581-588 (1990)), actin promoter (see, e.g., An, et al., The Plant J. 10:107 (1996)) and Zhang, et al., The Plant Cell 3:1155-1165 (1991)); Cassava vein mosaic virus promoters (see, e.g., WO 97/48819 and Verdaguer, et al., Plant Mol. Biol. 37:1055-1067 (1998)), the pPLEX series of promoters from Subterranean Clover Stunt Virus (WO 96/06932, particularly the S4 or S7 promoter), alcohol dehydrogenase promoter (e.g., pAdhlS (GenBank accession numbers X04049, X00581)), and the TR 1′ promoter and the TR2′ promoter which drive the expression of the 1′ and 2′ genes, respectively, of the T-DNA (Velten, et al., EMBO J. 3:2723-2730 (1984)). Tissue-specific promoters are promoters that direct a greater level of transcriptional expression in some cells or tissues of the plant than in other cells or tissue. Non-limiting examples of tissue-specific promoters include the phosphoenolpyruvate carboxylase (PEP or PPC1) promoter (Pathirana, et al., Plant J. 12:293-304 (1997), and Kausch, et al., Plant Mol. Biol. 45(1):1-15 (2001)), chlorophyll A/B binding protein (CAB) promoter (Bansal, et al., Proc. Natl. Acad. Sci. USA 89(8):3654-8 (1992)), small subunit of ribulose-1,5-bisphosphate carboxylase (ssRBCS) promoter (Bansal, et al., Proc. Natl. Acad. Sci. USA 89(8):3654-8 (1992)), senescence activated promoter (SEE1) (Robson, et al., Plant Biotechnol. J. 2(2):101-12 (2004)), and sorghum leaf primoridia specific promoter (RS2) (GenBank Accession No. EI979305.1). These promoters (PPC1, CAB, ssRBCS, SSE1, and RS2) are all active in the aerial part of a plant. Further, the PPC1 promoter is a strong promoter for expression in vascular tissue. Some examples of phloem specific promoters are the sucrose synthase-1 promoters (CsSUS 1p and CsSUS 1p-2) (Singer et al., Planta 234:623-637 (2011)) and the phloem protein-2 promoter (CsPP2) (Miyata et al., Plant Cell Report 31(11):2005-2013 (2012)) from Citrus sinensis. Alternatively, a plant-expressible promoter may also be a wound-inducible promoter, such as the promoter of the pea cell wall invertase gene (Zhang, et al., Plant Physiol. 112:1111-1117 (1996)).

Other types of RNA polymerase promoters that may be used are promoters from microorganisms, such as, but not limited to the bacteriophage T7 RNA polymerase promoter, yeast Galactose (GAL1) promoter, yeast glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter, yeast Alcohol Oxidase (AOX) promoter.

Other elements used to increase transcription expression in plant cells include, but are not limited to, an intron (e.g., hsp70 intron) at the 5′ end or 3′ end of the chimeric gene, or in the coding sequence of the chimeric dsRNA gene (such as, between the region encoding the sense and antisense portion of the dsRNA), promoter enhancer elements, duplicated or triplicated promoter regions, 5′ leader sequences different from the chimeric gene or different from an endogenous (plant host) gene leader sequence, 3′ untranslated sequences different from the chimeric gene or different from an endogenous (plant host) 3′ untranslated sequence.

The expression vector or cassette could contain suitable 3′ untranslated transcription regulation sequences (i.e., transcript formation and polyadenylation sequences). Potential polyadenylation and transcript formation sequences include those sequences in the nopaline synthase gene (Depicker, et al., J. Molec. Appl. Genetics 1:561-573 (1982)), the octopine synthase gene (Gielen, et al., EMBO J. 3:835-845 (1984)), the SCSV or the Malic enzyme terminators (Schunmann, et al., Plant Functional Biology 30:453-460 (2003)), and the T-DNA gene 7 (Velten and Schell, Nucleic Acids Research 13:6981-6998 (1985)).

The term “plant” includes whole plants, plant organs, progeny of whole plants or plant organs, embryos, somatic embryos, embryo-like structures, protocorms, protocorm-like bodies (PLBs), and suspensions of plant cells. Plant organs comprise, e.g., shoot vegetative organs/structures (e.g., leaves, stems and tubers), roots, flowers and floral organs/structures (e.g., bracts, sepals, petals, stamens, carpels, anthers and ovules), seed (including embryo, endosperm, and seed coat) and fruit (the mature ovary), plant tissue (e.g., vascular tissue, ground tissue, and the like) and cells (e.g., guard cells, egg cells, trichomes and the like). The class of plants that can be used in the method of the invention is generally as broad as the class of higher and lower plants amenable to the molecular biology and plant breeding techniques described herein, specifically angiosperms (monocotyledonous (monocots) and dicotyledonous (dicots) plants). It includes plants of a variety of ploidy levels, including aneuploid, polyploid, diploid, haploid and hemizygous. The genetically altered plants described herein are guayule plants.

Rubber yield may be expressed as a product of rubber content (% rubber) and biomass (dry weight/unit area). Thus, rubber yield may be improved by increasing either biomass and/or rubber content. The altered guayule described herein produce more rubber and have higher rubber content than non-altered guayule, thereby increasing the processing efficiency of the altered guayule shrub.

Because changes in PaAos functionality changes the amount of rubber produced by guayule, this invention also involves increasing a guayule's rubber production by reducing the amount of functional PaAos present in the genetically altered guayule (compared to the amount of functional PaAos present in non-altered guayule). In one embodiment, the genetically altered guayule has a mutation in PaAos, such as, a null mutation which results in (i) no protein is produced, (ii) a truncated protein is produced which has no functionality, or (iii) a full-length protein is produced which has no functionality. Other mutations simply reduce the functionality (activity) of PaAos. Non-limiting examples of mutations that reduce or eliminate PaAos functionality include (i) changing a codon encoding an amino acid to a stop codon (see Table 1 supra for the sequence of stop codons), (ii) changing the translation initiation codon (ATG) to any other codon to disrupt protein translation, (iii) changing a ribosome binding site's sequence to disrupt protein translation, (iv) changing one or more splice site codons to alter protein sequence, (v) deleting some or all of the gene's DNA sequence, (vi) inserting DNA into the gene, and (vii) changing one or more DNA codon sequences to encode non-conservative amino acids. Within SEQ ID NO: 9, nucleotides 34-36 encode ATG, the translation initiation codon for G7-11 guayule. Similarly, nucleotides 1-3 of SEQ ID NOs: 12 and 14 encode ATG, the translation initiation codon for cultivars PI 478652 and W6549, respectfully. Thus, a change in the nucleotide sequence of the equivalent codon in any other guayule would have the same result. Within PaAos, non-conservative amino acid substitutions at D318, 5332, E336, R339, 5359, 1408, 5411, and/or L459 (to name a few) result in PaAos with reduced functionality. One alters guayule DNA using the methods described herein and assesses changes in PaAos functionality via the methods described herein (e.g., assessing the amount of rubber produced by the altered guayule) or using methods known to one of ordinary skill in the art. One can utilize SNPs, antibodies, and other methods to identify the guayule that encode the altered amino acids.

Various methods exist to create a mutation. These methods are well-known to one of ordinary skill in the art. One method is by transforming the plant with a plasmid containing 5′ sequence and 3′ sequence of the gene and allowing a cross-over event to occur, thereby excising the DNA from the plant's genome that is between the plasmid's 5′ sequence and 3′ sequence. Also, one can use transposon-mediated mutation to delete or add DNA to PaAos which would result in the encoded protein having a reduced functionality compared to a non-altered PaAos. Two other methods involve using a chemical mutagen (such as ethyl methanesulfonate (EMS)) or physical agents (radiation, UV, or proton, for example) to generate genetic mutations in plant cells and/or germplasm. Also, one may use TALEN or CRISPR-Cas9 to mutate the sequence of the target gene (PaAos) such that a desired mutation is generated. One of ordinary skill in the art can also use targeted cleavage events to induce targeted mutagenesis, induce targeted deletions of cellular DNA sequences, and facilitate targeted recombination and integration at predetermined chromosomal locations to generate one or more of the null mutations discussed above or to reduce the mutated protein's functionality. Nucleotide editing techniques are well-known and described in Urnov, et al., Nature 435(7042):646-51 (2010); U.S. Patent Publications 2003/0232410, 2005/0208489, 2005/0026157, 2005/0064474, 2006/0188987, 2009/0263900, 2009/0117617, 2010/0047805, 2011/0207221, 2011/0301073, 2011/089775, 2011/0239315, and 2011/0145940; and International Publication WO 2007/014275, the disclosures of which are incorporated by reference in their entireties for all purposes. Cleavage occurs by using specific nucleases such as engineered zinc finger nucleases (ZFN), transcription-activator like effector nucleases (TALENs), or using the CRISPR/Cas9 system with an engineered crRNA/tracr RNA ('single guide RNA') to guide specific cleavage. U.S. Patent Publication 2008/0182332 describes the use of non-canonical zinc finger nucleases (ZFNs) for targeted modification of plant genomes; U.S. Patent Publication 2009/0205083 describes ZFN-mediated targeted modification of a plant EPSPS locus; U.S. Patent Publication 2010/0199389 describes targeted modification of a plant Zp15 locus and U.S. Patent Publication No. 20110167521 describes targeted modification of plant genes involved in fatty acid biosynthesis. In addition, Moehle, et al., Proc. Natl. Acad. Sci. USA 104(9):3055-3060 (2007) describes using designed ZFNs for targeted gene addition at a specified locus. U.S. Patent Publication 2011/0041195 describes methods of making homozygous diploid organisms. Information on CRISPR/Cas9 system is found, e.g., at en.wikipedia.org/wiki/CRISPR; neb.com/tools-and-resources/feature-articles/crispr-cas9-and-targeted-genome-editing-a-new-era-in-molecular-biology; and Cong, et al., Science, 339:819-823 (2013). Sigma-Aldrich (St. Louis, Mo.) and Origene Technologies, Inc. (Rockville, Md.) are among the companies that sell CRISPR/Cas9 kits.

After using any of these various methods to induce genetic alterations in a cell's genome, one induces the treated cells to grow into plants and then screen the plants using the methods described herein for PaAos having reduced or no functionality, and/or for reduced amounts of PaAos or no PaAos (via reduction in gene expression and/or mRNA translation and/or other mechanism), and/or for elevated production of rubber (compared to amounts present in non-altered plants). Thus, another embodiment of this invention is the generation of altered guayule having a genetic alteration in PaAos such that the altered guayule produces more rubber than produced by non-altered guayule.

Another embodiment of this invention is that one increases rubber production in guayule by increasing the amount of SA in altered guayule compared to the amount of SA present in untreated or non-altered guayule. One administers SA to guayule by spraying SA onto the guayule, drenching the soil around guayule with SA, adding SA to irrigation water which is then used to irrigate guayule. Another embodiment is to generate genetically altered guayule that produce an increased amount of SA than is produced by non-altered guayule by reducing the amount of functional PaAos in the genetically altered guayule. Such a reduction can be caused by a mutation in PaAos. The quantity (effective amount) of SA administered to the altered guayule being grown in tissue culture is the amount sufficient to generate a concentration in the tissue culture media ranging from approximately 0.1 nM to approximately 100 nM in one embodiment, from approximately 1 nM to approximately 100 nM solution in another embodiment, from approximately 5 nM to approximately 100 nM solution in another embodiment, and from approximately 10 nM to approximately 50 nM solution in another embodiment. For guayule plants in soil, from approximately 1 nM to approximately 100 nM SA solution in one embodiment, from approximately 5 nM to approximately 50 nM SA solution in another embodiment, or approximately 10 nM SA solution may be administered once, twice, or more per week. One can apply approximately 1 mL, approximately 10 mL, approximately 100 mL of the SA solution, depending on the SA concentration and the frequency of application. In one embodiment, 50 mL of 10 nM SA solution is applied twice weekly. To produce 10 nM SA solution, 0.0013812 mg SA is dissolved in 1 liter of 0.0000065% ethanol. To produce 100 nM SA solution, 0.013812 mg SA is dissolved in 1 liter of 0.0000065% ethanol. SA may be administered in a controlled release formulation, similar to children's liquid aspirin formulations or as a powder. SA can be administered early in a guayule plant's life (post-seedling stage which is approximately one month after germination of the seed), later in a guayule plant's life (several months prior to cut harvest), on a seasonal basis (during heat season, cold season, or both), or on a daily, weekly or monthly basis throughout the lifespan of the guayule plant. Administering SA to a guayule plant when exposed to cold temperatures (between approximately 7° C. and approximately 15° C. or between approximately 10° C. and approximately 15° C.; for approximately 8 hours per day), as occurs during the cold season, results in synergistically increase in rubber production. The term “administering SA to a guayule” and similar phrases means that exogenous SA is applied to the soil or plant or plant part.

Many techniques involving molecular biology discussed herein are well-known to one of ordinary skill in the art and are described in, e.g., Green and Sambrook, Molecular Cloning, A Laboratory Manual 4th ed. 2012, Cold Spring Harbor Laboratory; Ausubel et al. (eds.), Current Protocols in Molecular Biology, 1994—current, John Wiley & Sons; and Kriegler, Gene Transfer and Expression: A Laboratory Manual (1993). Unless otherwise noted, technical terms are used according to conventional usage. Definitions of common terms in molecular biology maybe found in e.g., Benjamin Lewin, Genes IX, Oxford University Press, 2007 (ISBN 0763740632); Krebs, et al. (eds.), The Encyclopedia of Molecular Biology, Blackwell Science Ltd., 1994 (ISBN 0-632-02182-9); and Robert A. Meyers (ed.), Molecular Biology and Biotechnology: a Comprehensive Desk Reference, VCH Publishers, Inc., 1995 (ISBN 1-56081-569-8).

The terms “approximately” and “about” refer to a quantity, level, value or amount that varies by as much as 30% in one embodiment, or in another embodiment by as much as 20%, and in a third embodiment by as much as 10% to a reference quantity, level, value or amount. As used herein, the singular form “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a bacterium” includes both a single bacterium and a plurality of bacteria.

The term “nucleic acid consisting essentially of”, “polynucleotide consisting essentially of”, and “RNA consisting essentially of”, and grammatical variations thereof, means a polynucleotide that differs from a reference nucleic acid sequence by 20 or fewer nucleotides and also perform the function of the reference polynucleotide sequence. Such variants include sequences which are shorter or longer than the reference nucleic acid sequence, have different residues at particular positions, or a combination thereof.

Having now generally described this invention, the same will be better understood by reference to certain specific examples and the accompanying drawings, which are included herein only to further illustrate the invention and are not intended to limit the scope of the invention as defined by the claims. The examples and drawings describe at least one, but not all embodiments, of the inventions claimed. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

EXAMPLE 1 Construction of Genetically Altered Guayule

To better understand the role of PaAos in rubber synthesis, genetically altered P. argentatum plants are generated in which either PaAos is over-expressed or PaAos is silenced by RNAi. The various plasmids used to achieve the overexpression or silencing of PaAos in guayule are shown in FIG. 1. To generate these plasmids, the guayule Aos (PaAos) is amplified by PCR using genomic DNA as a template. The primers used to amplify PaAos are designed from the cDNA PaAos sequence published in NCBI database (GeneBank accession no. X78166.2) and have the following sequences: forward primer 5′-cttaagaggtggtATGGACCCATCGTCTAAACCC-3′ (SEQ ID NO: 1) and reverse primer 5′-ggatccTCATATACTAGCTCTCTTCAGGG-3′ (SEQ ID NO: 2). The nucleotides in lower case and underlined in the forward primer are the recognition nucleotides for restriction enzyme AflII; the nucleotides in lower case and underlined in the reverse primer are the recognition nucleotides for restriction enzyme BamHI. The PCR cycle program is the following: 94° C. for 2 minutes (initial heating step) and PaAos is amplified at 40 cycles of 94° C. for 30 seconds (denaturation), 71° C. for 30 seconds (annealing) and 68° C. for 1 minute (extension) and an additional 5 minutes extension at 68° C. The resulting amplicon is purified and subcloned into pGEM T Easy vector (Promega, Madison, Wis.) using manufacturer's recommended protocol and sequenced to confirm the sequence of the plasmids. The cDNA sequence is in SEQ ID NO: 9 and the amino acid sequence is in SEQ ID NO: 10. Subsequently, the PaAos amplicon is cut using AflII and BamHI (Promega, Madison, Wis.). Plasmid pND6 has a Nos promoter driving the NPTII gene for conferring kanamycin resistance and a potato ubiquitin promoter (Garbarino and Belknap, Plant Mol. Biol. 24:119-127 (1994)) controlling the GUSplus gene (CambiaLabs, Canberra, Australia). See FIG. 1. Plasmid pND6-Aos (FIG. 1) is generated by replacing the GUSplus gene in pND6 with cDNA PaAos sequence (SEQ ID NO: 9). Plasmid pND6-AosiL (FIG. 1) is generated by replacing the GUSplus gene in pND6 with an inverted repeat of a partial cDNA PaAos sequence (SEQ ID NO: 11) containing a loop sequence of the Bar gene between the inverted repeat of the partial cDNA PaAos sequence; the complete sequence replacing GUSplus is SEQ ID NO: 45. The plasmids pND6, pND6-AosiL, and pND6-Aos are used to transform Agrobacterium EHA101 competent cells using the protocol described in Hood, et al., J. Bacteriol. 168:1291-1301 (1986).

The transformed Agrobacterium EHA101 either harboring pND6, pND6-AosiL, or pND6-Aos are used to transform guayule G7-11 using the protocols set forth below. See also Dong, et al. (2006) and Dong, et al., Industrial Crops and Products 46:15-24 (2013). For Agrobacterium transformation, the overnight Agrobacterium culture are prepared by inoculating 50 μL glycerol stock into a 50 mL Falcon tube containing 5 mL LB medium plus 40 mg/L rifampcin and 200 mg/L spectinomycin, and shaking at 200 rpm at 28° C. The suspension then is centrifuged for 15 minutes at 1600 × g at room temperature. The supernatant is discarded, and the pellet is re-suspended in 25 mL of inoculation solution (1/10 MS salts plus BA (2 mg/L), NAA (0.5 mg/L), glucose (10 g), acetosyringone (200 μM), pluronic F68 (0.05%), pH=5.2 (PhytoTechnology Labs, Shawnee Mission, Kans.)). For leaf transformation, leaf sections are cut from the plants in the Magenta boxes (Caisson Labs, Smithfield, Utah). The adaxial side of each leaf is placed facing up in a Petri dish containing 5 ml Agrobacterium suspension. The leaf is cut into ˜10 mm strips and immediately placed in an empty Petri dish in non-overlapping manner When this Petri dish is full, all leaf strips are blotted with the filter paper and placed into another empty Petri dish. The Petri dish is sealed by parafilm and left in the dark at room temperature. The co-cultivation is replaced by this co-desiccation according to Cheng, et al., In Vitro Cell Dev. Biol. Plant, 39, 595-604 (2003). After three days, leaf strips are transferred to MSB1T (MS medium with BA (1 mg/L), sucrose (30 g/L), phytagel (3 g/L), and timentin (400 mg/L)) (Cheng, et al., Plant Cell Rep., 17(8):646-649 (1998)) for recovery at low light for 5 days. The leaf strips are then transferred to MSB1TK30 (MS medium containing BA (1 mg/L), sucrose (30 g/L), phytagel (3 g/L), timentin (250 mg/L), and kanamycin (30 mg/L)) for selection under low light for two weeks. The leaf strips are then subcultured every 2 weeks under high light till green shoots emerged. Green shoots 10 mm and longer are transferred to 1/2MS10.1TK10 for rooting (same as 1/2MSI0 but with timentin (250 mg/L) and kanamycin (10 mg/L)). After 2-4 weeks, the rooted plantlets are micropropogated and subsequently transplanted into soil.

While the genetically altered guayule are still growing in tissue culture under selection, the genetically altered plants are screened for integration of the expression vectors, pND6-Aos (PaAos in forward orientation; SEQ ID NO: 9), pND6-AosiL (SEQ ID NO: 45 which contains a portion of reverse complement of PaAos (SEQ ID NO: 11)), and pND6 (negative control). DNA is extracted from genetically altered plants using Sigma Kit (Sigma-Aldrich, St. Louis, Mo.). Approximately 150 mg leaf tissue (3 leaf tissues) are cut from the plants grown in tissue-cultured, placed into 2 mL tubes and snapped-frozen in liquid nitrogen. A bead is added to pulverize the tissue into a fine powder at a frequency of 30/s for 1 minute using the mixer mill MM 400 tissue lyser (Verder Scientific, Inc., Newtown, Pa.).

PCR is carried out in 50 tit mixture containing Taq 2X Master Mix (New England Biolabs, Ipswich, MA), 200 ng guayule genomic DNA or 20 pg plasmid DNA, and 100 ng of PaAos specific primers; namely SEQ ID NOs: 1 and 2 for guayule transformed with pND6-Aos; and SEQ ID NOs: 3 and 4 for guayule transformed with pND6-AosiL. See FIG. 2. After heating the samples to 94° C. for 2 minutes, the reaction proceeds with 35 cycles of 94° C. for 30 seconds, 71° C. to amplify the PaAos in the overexpression lines (pND6-Aos) for 30 seconds or 56° C. for the PaAos in the RNAi lines (pND6-AosiL) for 30 seconds, and 68° C. for 1 minute. A final elongation step is carried out at 68° C. for 5 minutes. PCR products are separated by electrophoresis on a 1% (w/v) agarose gel. The band for the overexpression lines is at ˜1.4 kbp, as expected; the band for the RNAi lines is at -0.5 kbp as expected. The genetically altered guayule plants harboring the empty plasmid (pND6 (negative control)) are confirmed by GUS staining (Karcher, S., ABLE 23:29-42 (2002)). Briefly, plant tissues are placed in a 50 mL tube containing GUS assay solution (1 mM X-Gluc (5-bromo-4-chloro-3-indolyl) B-D-glucuronic acid in 50 mM Na₂HPO₄, pH 7.0 and 0.1% Triton X-100). The reaction is incubated at 37° C. for 1 hour followed by washing for 30 minutes with 70% ethanol to extract the chlorophyll.

Example 2 Determination of RNA Expression Levels in Genetically Altered Plants

Guayule containing intact PaAos (non-altered; G7-11) and genetically altered guayule containing one of the plasmids (pND6, pND6-Aos, or pND6-AosiL) are further screened to determine the RNA level (see Table 3). Leaves from the various genetically altered plants (which are grown in tissue culture) are collected and snap-frozen in liquid nitrogen for RNA extraction. RNA is extracted using TRIzol® according to manufacturer's recommended protocol (Ambion, Pittsburg, Pa.). RNA concentration is quantified with the NanoDrop ND1000 (ThermoScientific, Wilminton, Del.). RNA cleanup is performed using the RNeasy MinElute Cleanup kit according to manufacturer's recommended protocol (Qiagen Inc., Valencia, Calif.). The RNA is eluted with 30-50 tit of RNase-free water along with on-column DNase 1 treatment.

Using the RNA isolated from the leaves of the genetically altered plants, cDNA is generated using iScript cDNA synthesis kit (Bio-Rad, Hercules, CA) according to the manufacturer's recommended protocol for semi-quantitative PCR and real-time quantitative PCR (qRT-PCR). An amount of 1 μg of RNA is used in the 20 mL reaction mixture. For qRT-PCR, 2 μL of the diluted cDNA (1:20) is used in a 15 μL reaction mixture. In the qRT-PCR volume, 7.5 mL of iQ SYBR® Green Supermix is used (Bio-Rad, Hercules, Calif.). The qRT-PCR is run using the 7500 Fast Real-Time PCR system (Applied Biosystem, Waltham, Mass.) with the following thermal cycle: 95° C. pre-incubation for 3 minutes; amplification is performed for 40 cycles at 95° C. for 15 seconds and at 60° C. for 30 seconds; the dissociation stage is set for 95° C. for 15 seconds, at 60° C. for 1 minute, and at 95° C. for 15 seconds. Each qRT-PCR run is performed with three independent tissue samples, each sample having two technical replicates. The 18S gene (-200 bp) is used as an internal control. The primers used for each sequence, PCR reaction conditions, and the expected amplicon size are contained in FIG. 2. Crossing point value, which is the point at which the fluorescence crosses the threshold, and melting curve analyses are noted. The melting curve data are collected for all genes to ensure a single peak, indicating amplification of a specific region by a pair of primers. The relative expression values are calculated using the 2(-Delta C(T)) method (Livak and Schmittgen, Methods, 25:402-408 (2001)). See Table 3 below.

TABLE 3 P. argentatum Average Relative Genotypes Expression of Aos G7-11 1.02 ± 0.2  pND6-10 1.14 ± 0.2  pND6-12 1.02 ± 0.3  pND6-29 1.04 ± 0.2  pND6-32 1.00 ± 0.3  pND6-33 1.11 ± 0.3  pND6-35 0.90 ± 0.2  pND6-41 0.91 ± 0.2  pND6-AosiL₅₋₁ 0.39 ± 0.1*  pND6-AosiL₇₋₂ 0.49 ± 0.1*  pND6-AosiL₈₋₁ 0.53 ± 0.1*  pND6-AosiL₉₋₁₅ 0.44 ± 0.1*  pND6-AosiL₉₋₁₆ 0.37 ± 0.04* pND6-AosiL₁₂₋₁ 0.55 ± 0.1*  pND6-AosiL₁₂₋₃ 0.48 ± 0.1*  pND6-AosiL₁₃₋₂ 0.55 ± 0.05* pND6-AosiL₁₅₋₃ 0.36 ± 0.1*  pND6-AosiL₁₅₋₄ 0.48 ± 0.2*  pND6-Aos₄₋₁ 2.15 ± 0.1** pND6-Aos₄₋₂ 2.11 ± 0.3** pND6-Aos₅₋₁ 2.29 ± 0.4** pND6-Aos₇₋₁ 2.40 ± 0.6** pND6-Aos₇₋₃ 2.11 ± 0.2** pND6-Aos₈₋₂ 2.15 ± 0.2** pND6-Aos₁₀₋₁ 2.44 ± 0.7** pND6-Aos₁₀₋₂ 2.12 ± 0.4** pND6-Aos₁₁₋₅ 2.30 ± 0.3** pND6-Aos₁₄₋₂ 2.23 ± 0.1** G7-11 = wild-type control; pND6 = empty vector (pND6 without Aos); pND6-AosiL = PaAos is knocked-down/silenced; pND6-Aos = PaAos is over-expressed Results are average of three independent plants, each plant having three technical replicates. * and ** indicate significant difference in comparison to G7-11 guayule and/or pND6 (controls) at p > 0.05 and 0.005, respectively.

Next, to gain more insight as to where the PaAos is spatially located, the expression pattern of PaAos in various guayule tissues is analyzed using qRT-PCR. Total RNA is extracted from leaves, petiole, stem, root, young flower, mature flower, peduncle, stembark of 8-week-old tissue-cultured genetically altered plants as well as 2-month-old greenhouse grown genetically altered plants using the protocol described above. qRT-PCR is performed as described above on these samples of total RNA. Primers (SEQ ID NOs: 7 and 8 in FIG. 2) are designed to amplify ˜200 bp PCR product in PaAos coding sequence. The expression level for each tissue are compared to the tissue cultured and greenhouse leaf tissues, respectively. The 18S gene (-200 bp) (forward primer is SEQ ID NO: 5 and reverse primer is SEQ ID NO: 6, described supra and in FIG. 2) is used as an internal control. As shown in Table 4, infra, the largest level of PaAos expression is present in the stem, root and stembark tissues, suggesting that these tissues are sites in which PaAos is functioning.

TABLE 4 Growth Conditions: MS Medium Greenhouse Tissue Source Relative Expression Leaf 0.98 ± 0.1 1.04 ± 0.2 Petiole  0.31 ± 0.06 0.41 ± 0.1 Stem 2.27 ± 0.2 3.37 ± 0.4 Root 2.47 ± 0.2 3.74 ± 0.3 Young Flower no data 1.23 ± 0.4 Mature Flower no data 0.69 ± 0.2 Peduncle no data 0.25 ± 0.1 Bark no data 4.49 ± 1.2 The error bars represent tissues collected from 3 individual plants.

Example 3 Rubber Quantification in Tissue

Rooted plantlets (genetically altered, empty vector transformed (pND6 without PaAos), and wild-type control) from transferred shoot tips are grown on half-strength MS medium (PhytoTechnology Laboratories, Overland Park, Kans.) in Magenta boxes (Caisson Labs, Smithfield, Utah) for 6 weeks. The top part of the plantlets are separated from the medium and lyophilized for 48 hours. The dried tissues are placed in a 50 mL stainless steel grinding jar containing grinding ball, frozen in liquid nitrogen for 5 minutes and finely ground using the Retsch mixer mill MM 400 at a frequency of 30/second for 1 minute (Verder Scientific Inc., Newtown, Pa.). Three hundred milligrams (0.3 g) of pulverized tissues are partitioned with Ottawa sand (Fisher Scientific, Fair Lawn, New Jersey) and loaded into 11 mL stainless steel extraction cells (Dionex, Sunnyvale, Calif.). Three sequential extractions are performed using the Accelerated Solvent Extractor (ASE 2000; Dionex, Sunnyvale, Calif.): 1. Acetone: to remove resinous material and the low molecular weight organic solubles; 2. Methanol: to remove chlorophyll and other alcohol-soluble materials; 3. Cyclohexane: to remove rubber. Natural rubber is quantified gravimetrically. The percent (%) rubber is the amount (% dw) of cyclohexane extract from 0.3 g dried tissue. The pND6-AosiL plants have 1.5 to 2 times more rubber than G7-11, pND6 and pND6-Aos in tissue-cultured environment (Table 5). In Table 5, the rubber content is quantified from leaf and stems of the indicated guayule genotypes grown in MS media.

TABLE 5 Rubber content of guayule plant shoots determined by Accelerated Solvent Extraction P. argentatum Average Rubber Genotypes Content (%) G7-11.1 1.01 ± .01 G7-11.2 1.11 ± .02 pND6-12 1.13 ± 0.2 pND6-33 1.10 ± 0.1 pND6-35 1.04 ± 0.2 pND6-AosiL₅₋₁  1.8 ± 0.1* pND6-AosiL₇₋₂   2.0 ± 0.3** pND6-AosiL₈₋₁    2.1 ± 0.04*** pND6-AosiL₈₋₂   1.7 ± 0.1** pND6-AosiL₉₋₁₅   1.7 ± 0.02** pND6-AosiL₉₋₁₆  2.3 ± 0.4* pND6-AosiL₁₂₋₁  2.46 ± 0.3* pND6-AosiL₁₂₋₃    1.62 ± 0.002*** pND6-Aos₄₋₁ 0.96 ± 0.2 pND6-Aos₄₋₂ 0.85 ± 0.1 pND6-Aos₅₋₁ 1.09 ± 0.1 pND6-Aos₅₋₂ 1.23 ± 0.1 pND6-Aos₇₋₁ 0.96 ± .02 pND6-Aos₈₋₂ 1.23 ± 0.1 pND6-Aos₁₁₋₅ 1.23 ± 0.1 Note: The rubber content is quantified from shoots (leaves + stems) of guayule genotypes grown in MS media. Error bars represent three biological plants with three technical replicates each. *, ** and *** indicate significant difference in comparison to G7-11 guayule and/or pND6 (controls) at p > 0.05, 0.005 and 0.0005, respectively.

Next, the genetically altered guayule plants are transplanted into soil and grown for 2 months under 27° C. (16 h)/25° C. (8 h) and 27° C. (16 h)/10° C. (8 h) in growth chamber conditions, representing a microcosm of what guayule plants experience in the field during winter. Under these conditions, pND6-AosiL plants also exhibited elevated rubber content, having up to 31% times more rubber in comparison with G7-11, pND6 and pND6-Aos plants (Table 6). In Table 6, the rubber content is quantified from shoots and roots of the indicated guayule genotypes grown in soil. These plants are approximately 4 months old when rubber content is analyzed (tissue culture (approx. 1.5 months), greenhouse (approx. 1 month), and growth chamber (approx. 2 months)).

TABLE 6 Rubber content of guayule plant tissue determined by Accelerated Solvent Extraction Average Rubber Content (%) Shoot Root P. argentatum 27° C. (16 h)/ 27° C. (16h)/ 27° C. (16h)/ 27° C. (16h)/ Genotypes 25° C. (8 h) 10° C. (8h) 25° C. (8h) 10° C. (8h) G7-11.1 1.22 ± 0.09 1.13 ± 0.11 1.10 ± 0.04 0.95 ± 0.10 G7-11.2 1.06 ± 0.12 1.37 ± 0.09 0.63 ± 0.12 0.71 ± 0.09 pND6-12 1.04 ± 0.18 1.31 ± 0.06 0.65 ± 0.07 0.72 ± 0.16 pND6-33 0.90 ± 0.06 1.14 ± 0.12 0.62 ± 0.08 0.82 ± 0.10 pND6-35 1.18 ± 0.08 1.27 ± 0.10 1.09 ± 0.06 0.94 ± 0.03 pND6-AosiL₇₋₂   1.49 ± 0.07***   1.86 ± 0.11*** 0.56 ± 0.03  1.26 ± 0.09** pND6-AosiL₈₋₁ 1.48 ± 0.05   1.91 ± 0.07*** 0.78 ± 0.14  1.19 ± 0.04** pND6-AosiL₉₋₁₆   1.46 ± 0.04***   2.01 ± 0.08*** 0.66 ± 0.12  1.16 ± 0.02** pND6-AosiL₁₂₋₁  1.55 ± 0.07*   1.80 ± 0.05***   1.26 ± 0.04***  1.52 ± 0.07** pND6-Aos₄₋₁ 0.97 ± 0.26 1.13 ± 0.2  0.57 ± 0.05 0.79 ± 0.09 pND6-Aos₄₋₂ 1.21 ± 0.10 1.30 ± 0.08 1.05 ± 0.10 0.94 ± 0.11 pND6-Aos₅₋₁ 0.98 ± 0.30 1.04 ± 0.12 0.54 ± 0.11 0.62 ± 0.10 pND6-Aos₇₋₁ 0.96 ± 0.30 1.15 ± 0.14 0.57 ± 0.06 0.55 ± 0.08 Note: The rubber content is quantified from shoots and roots of guayule genotypes grown in soil. Plants are transferred to soil from tissue culture and are grown in a growth chamber environment. Error bars represent three biological plants with three technical replicates each. *, ** and *** indicate significant difference in comparison to G7-11 and/or pND6 (controls) at p > 0.05, 0.005 and 0.0005, respectively.

Because rubber is also accumulated in root tissue, the rubber content in the root tissues is also quantified. For the root rubber content, the consistent, significant difference is only under 27° C. (16 h)/10° C. (8 h) in which pND6-AosiL guayule have an increased in rubber content compared with the controls and pND6-Aos (Table 6). The data in Table 6 demonstrate that the combination of cold temperature and silencing PaAos is synergistic, causing guayule to produce a greater amount of rubber than guayule exposed to just cold temperature or to just PaAos silencing. For example, cold treatment alone increased shoot rubber content in the control (pND6-12) by 19%—from an average of 1.04% to 1.24%. But cold treatment of the Aos-downregulated plants (pND6-AosiL) increased rubber by 27%—from average 1.50% to 1.90%. In root tissues, cold treatment increased the rubber content for the control (pND6-12) by 5.1% (from 0.79 to 0.83% rubber), but cold treatment of the Aos-downregulated plants (pND6-AosiL) increased rubber by 57%—from average 0.82% to 1.28%. See Table 7, infra. From the ASE results, the increased in rubber content is very apparent in the pND6-AosiL genotypes.

TABLE 7 Average Rubber Content (%) Shoot Root P. argentatum 27° C. (16 h)/ 27° C. (16 h)/ 27° C. (16 h)/ 27° C. (16 h)/ Genotypes 25° C. (8 h) 10° C. (8 h) 25° C. (8 h) 10° C. (8 h) pND6-12 1.04 1.24 0.79 0.83 pND6-AosiL₇₋₂ 1.50 1.90 0.82 1.28 pND6-Aos₄₋₁ 1.03 1.16 0.68 0.73

Example 4 Protein Detection in Rubber Particles

Guayule washed rubber particles (WRPs) are isolated from genetically altered guayule lines (pND6-AosiLand pND6-Aos) and non-altered guayule using the protocol set forth in Cornish and Backhaus, Phytochemistry, 29: 3809-3813 (1990). Rubber particles are extracted from non-altered and genetically altered 1 year old greenhouse plants. First, ˜60 g to ˜70 g of stembark tissues are peeled off from the plant, grounded with a blender containing cold-extraction buffer, and further purified with cold-washed buffer three times by centrifugation. The protein extracts (1 mg) are run on an SDS-PAGE and detected with silver staining. On the SDS-PAGE gel, endogenous Aos protein runs as ˜53 kDa in the non-altered and overexpressed plants but not in the RNAi lines. To determine the dry weight of the WRPs, 50 tit of the protein extracts are aliquoted 3× on a weighing paper, oven-dried over-night in a 60° C. incubator and weighed the next day. Generally, approximately 0.5 mg/tit to approximately 1.5 mg/_(t)it WRPs are extracted.

Example 5 Hormone Production

PaAos is an enzyme in the biosynthetic pathway that produces several different plant hormones, including jasmonic acid, SA, abscisic acid, gibberellin A20, gibberellin A₁, and gibberellin A3. As such, the amount of these hormones is quantified in genetically altered (pND6-AosiL and pND6-Aos), empty vector transformed (pND6 without PaAos; control), and wild-type (G7-11, control) tissue-cultured guayule plants using the protocol described in Pan et al., Nature Protocols 5:986-992 (2010). See Table 8, infra. Briefly, leaves and stems are snap-frozen and ground to powder with mortar and pestle. Solvent extraction solution containing 2-propanol/H₂O/concentrated HCl (2:1:0.002; vol/vol/vol) and internal standards are added to ˜50 mg of pre-weighed tissues. After solvent extraction, sample concentration and re-dissolution, 50 μL of the sample solution is placed into the liquid chromatography-tandem spectrometry (Agilent GC-MS 5977A; Agilent Technologies, Santa Clara, Calif.) for hormone analysis. Three biological plants, with three technical replicates of each plant, are used.

TABLE 8 Concentration (ng/gfw) P. argentatum Jasmonic Salicylic Abscisic Gibberellin Gibberellin Gibberellin Genotypes Acid Acid Acid A₂₀ A₁ A₃ G7-11 5.36 ± 1.2   5.50 ± 0.8 11.01 ± 1.9  15.95 ± 0.7  9.95 ± 0.07 3.52 ± 0.2  pND6-12 1.57 ± 0.1   4.89 ± 0.6 7.05 ± 0.8  14.11 ± 1.2  12.39 ± 2.2  2.19 ± 0.01 pND6-33 4.76 ± 1.0   5.04 ± 0.1 7.24 ± 0.3  13.86 ± 2.6  12.70 ± 2.3  1.79 ± 0.09 pND6-35 1.96 ± 0.4   5.6 ± 0.5 7.10 ± 0.6  14.41 ± 1.2  14.65 ± 0.2  2.16 ± 0.3  pND6-AosiL₇₋₂ 0.57 ± 0.1**  9.51 ± 0.5* 4.71 ± 0.6* 9.63 ± 1.2* 5.13 ± 0.8* 0.86 ± 0.3* pND6-AosiL₉₋₁₆ 0.57 ± 0.01** 7.65 ± 0.2* 2.96 ± 0.3* 8.85 ± 2.1*  7.81 ± 0.2** 0.80 ± 0.3* pND6-AosiL₁₂₋₁ 0.68 ± 0.05** 9.65 ± 1.1* 3.64 ± 0.5* 10.59 ± 0.2*  6.75 ± 1.1*  1.32 ± 0.07* pND6-Aos₄₋₁ 1.48 ± 0.2   4.03 ± 0.7  9.13 ± 1.71 15.49 ± 0.6  10.78 ± 0.1  1.93 ± 0.06 pND6-Aos₄₋₂ 3.25 ± 0.2   4.76 ± 0.6  13.9 ± 1.3  no data 14.63 ± 2.7  1.80 ± 0.1  pND6-Aos₇₋₁ 1.41 ± 0.3   5.50 ± 0.02 8.84 ± 0.3  13.64 ± 1.2  13.96 ± 0.01  1.84 ± 0.1  ±represent three biological plants with three technical replicates each plant. * and **indicate significant difference in comparison to G7-11 and/or pND6 (controls) at p > 0.05 and 0.005, respectively.

As evident in Table 8, the amount of jasmonic acid, abscisic acid and gibberellic acids are reduced in the pND6-AosiL guayule compared to the amount in the controls (wild-type (G7-11) and empty vector transformed plants) and pND6-Aos guayule. Conversely, the SA content is elevated in pND6-AosiL compared to the controls and pND6-Aos lines. These results suggest that knocking down PaAos expression not only reduces production of jasmonic acid but also affects the level of other hormones as well.

Example 6 Plant Architecture and Photosynthetic Rates

Three independent events from each of the overexpression (pND6-Aos) and of the silenced (pND6-AosiL) lines; as well as two pND6 and one wild-type (G7-11) controls are selected for further studies. pND6-AosiL plants grown in greenhouse (data not shown) and growth chamber conditions are bigger (see FIG. 3)), have darker green leaves (data not shown), and increased chlorophyll measurement than the wild type and other genetically altered plants (see FIG. 4). As demonstrated in FIG. 3, under 27° C. (16 h)/25° C. (8 h) and 27° C. (16 h) /10° C. (8 h) environments, pND6-AosiL plants are significantly taller and wider in both conditions. These plant architectural traits reflect the fact that pND6-AosiL plants are larger and have more shoot and root biomass.

pND6-AosiL genotypes have also a greater number of stems than the wild-type and empty vector controls. Well-branched guayule plants are an indicator of having increased rubber yield because of the presence of more sink tissue available to store rubber. Additionally, the mature stembark tissues in pND6-AosiL have thicker diameter (ranging from approximately 35% to approximately 54%) under both 27° C. (16 h)/25° C. (8 h) and 27° C. (16 h)/10° C. (8 h) in comparison to the controls and pND6-Aos. See FIG. 5.

Based on this observation, the photosynthetic rate of the plants is measured using LI-COR 6400×t (LI-COR Biosciences, Lincoln, Neb.) to measure the photosynthetic rate. Measurements are taken between 0900 to 1200h. Fully expanded middle leaf are clamped on the Li-Cor head. After the measured and set parameters are stabilized, the reading is taken. The middle leaf position is chosen because this position shows significant differences based on chlorophyll meter measurements, FIG. 4. (SPAD-502; Minolta Camera Ltd., Japan). The pND6-AosiL plants exhibit higher photosynthetic rate (23-31%) in comparison to G7-11, pND6 and pND6-Aos plants (Table 9, infra). Additional physiological measurements reveal that pND6-AosiL stomatal limitation is one of the factors involved in the higher photosynthetic rate as pND6-AosiL plants show higher stomatal conductance and transpiration rate when compared to G7-11, pND6 and pND6-Aos plants (Table 9, infra). Furthermore, chlorophyll fluorescence measurements clearly show PSII and ETR parameters used for elucidating the efficiency of PSII are significantly higher than G7-11, pND6 and pND6-Aos plants (Table 9, infra) in both 27° C. (16 h)/25° C. (8 h) and 27° C. (16 h)/10° C. (8 h) treatment conditions. Having higher PSII and ETR indicate that amount of light energy absorbed and carbon assimilated is available more in pND6-AosiL plants to convert into energy for the plant to use (i.e., growth and development as well as rubber production) compared to the controls and pND6-Aos plants. Meanwhile, the NPQ measurements for the pND6-AosiL plants are lower under the 27° C. (16 h) /25° C. (8 h) condition and higher under the 27° C. (16 h)/10° C. (8 h) treatment in comparison with the controls and pND6-Aos plants. Having higher NPQ suggests that pND6-AosiL have improved heat dissipation ability compared to G7-11, pND6 and pND6-Aos plants which could help prevent lipid or other cell membrane damage under environmental stress.

TABLE 9 P. argentatum Genotypes Pn g € ΦPSII ETR NPQ 27° C. (16 h)/25° C. (8 h) G7-11 5.75 ± 0.8 0.093 ± 0.03 2.33 ± 0.6 0.146 ± 115.73 ± 1.97 ± 0.015 11.3 0.2 pND6-10 6.29 ± 0.7 0.110 ± 0.03 2.74 ± 0.6 0.141 ± 111.1 ± 1.74 ± 0.015 11.6 0.1 pND6-12 6.20 ± 0.8 0.109 ± 0.02 2.66 ± 0.5 0.145 ± 114.4 ± 1.90 ± 0.015 12.1 0.2 pND6-AosiL ₇₋₁ 8.56 ± 0.147 ± 3.41 ± 0.196 ± 165.2 ± 1.33 ± 0.6*** 0.01*** 0.3*** 0.027* 10.7*** 0.2*** pND6-AosiL ₈₋₁ 8.40 ± 0.155 ± 3.67 ± 0.180 ± 141.4 ± 1.27 ± 0.6*** 0.02*** 0.4*** 0.008* 6.2** 0.2*** pND6-AosiL ₉₋₁₆ 7.96 ± 0.162 ± 3.57 ± 0.186 ± 134.4 ± 1.19 ± 0.5*** 0.03*** 0.5*** 0.018* 3.3** 0.3*** pND6-Aos₄₋₁ 5.62 ± 0.9 0.110 ± 0.04 2.59 ± 0.7 0.133 ± 104.7 ± 6.7 1.92 ± 0.008 0.3 pND6-Aos₅₋₁ 5.70 ± 0.8 0.110 ± 0.04 2.60 ± 0.7 0.133 ± 104.7 ± 6.7 1.95 ± 0.008 0.3 pND6-Aos₇₋₁ 5.87 ± 0.9 0.113 ± 0.04 2.65 ± 0.7 0.137 ± 107.7 ± 6.3 2.07 ± 0.008 0.4 27° C. (16 h)/10° C. (8 h) G7-11 2.23 ± 0.5 0.054 ± 0.02 1.31 ± 0.4 0.070 ± 55.4 ± 5.4 1.58 ± 0.007 0.2 pND6-10 2.04 ± 0.4 0.057 ± 0.02 1.55 ± 0.3 0.064 ± 50.7 ± 4.9 1.56 ± 0.006 0.2 pND6-12 2.28 ± 0.4 0.065 ± 0.03 1.67 ± 0.7 0.066 ± 51.6 ± 2.7 1.51 ± 0.003 0.3 pND6-AosiL ₇₋₁ 4.14 ± 0.104 ± 2.54 ± 0.104 ± 81.0 ± 2.29 ± 0.4*** 0.02*** 0.4*** 0.011*** 8.2*** 0.3* pND6-AosiL ₈₋₁ 4.15 ± 0.112 ± 2.71 ± 0.102 ± 77.0 ± 2.33 ± 0.4*** 0.05*** 0.8*** 0.013*** 4.5*** 0.2** pND6-AosiL ₉₋₁₆ 4.14 ± 0.101 ± 2.60 ± 0.101 ± 79.4 ± 1.95 ± 0.6*** 0.03*** 0.5*** 0.009*** 6.9*** 0.1** pND6-Aos₄₋₁ 2.27 ± 0.5 0.059 ± 0.02 1.51 ± 0.3 0.065 ± 60.4 ± 5.5 1.35 ± 0.011 0.3 pND6-Aos₅₋₁ 2.97 ± 0.3 0.069 ± 0.01 1.81 ± 0.2 0.077 ± 58.5 ± 6.3 1.25 ± 0.007 0.2 pND6-Aos₇₋₁ 2.45 ± 0.6 0.063 ± 0.01 1.93 ± 0.3 0.065 ± 50.1 ± 5.8 1.44 ± 0.010 0.2 Pn = net photosynthetic rate; g = stomatal conductance; E = Transpiration rate; ΦPSII = Efficiency of Photosystem II; ETR = Electron Transport Rate; NPQ = Non-photochemical quenching *, ** and ***indicate significant difference in comparison to G7-11 and/or pND6 (controls) at p > 0.05, 0.005 and 0.0005, respectively.

Example 7 Quality of Natural Rubber from pND6-AOSiL Plants

The length of the polymer chain, a.k.a. rubber molecular weight, is the primary determinant of quality in natural rubber. Gel permeation chromatography (GPC) is used to measure the molecular weight of rubber from guayule tissue culture plants' extracts. Cyclohexane extractables collected from ASE (see Example 3 and Table 5 supra) are re-suspended in approximately 3 mL of tetrahydrofuran (THF) overnight with gentle shaking (Multi-Purpose Rotator, Thermo Scientific, Waltham, Mass.). The solution is syringe-filtered through a 1.6 μm glass microfiber GF/A filter (Whatman GE Healthcare, Piscataway, N.J.), then injected into a Hewlett Packard 1100 series HPLC (1.0 mL/min flow rate, 50 μL injection volume, THF continuous phase) and size exclusion separated by two Agilent PL gel 10 μm Mixed-B columns in series (35° C.) (Santa Clara, Calif.). The resulting chromatograms are used to calculate the rubber molecular weight shown in FIG. 6 (using Astra software (Wyatt Technology Corp., Santa Barbara, Calif.)). The molecular weight of natural rubber from three pND6-AosiL transformed guayule plants (silenced) is greater than from wild-type guayule line G7-11, two negative control pND6 transformed guayule plants and three pND6-Aos transformed guayule plants (overexpressed) indicating better quality rubber in the PaAos silenced guayule plants. In FIG. 6, the asterisks (*) and (**) above the three pND6-AosiL transformed guayule plant lines indicate significant difference in comparison to the negative control pND6 transformed guayule plant lines at p >0.05 and p >0.005, respectively.

Example 8 Exogenous Salicylic Acid (SA) Addition Reduces PaAos Gene Expression

The effect of SA on guayule PaAos gene expression is tested in wild-type guayule G7-11 plants. SA is added to the growth medium (K0) in tissue culture at different concentrations, 0 nM, 10 nM and 100 nM. Shoot tips are transferred to the growth media, and plants are grown for 8 weeks. The rubber content of the plant tissues is determined by standard procedures (ASE, see Example 3 supra). In comparison to 0 nM of SA, the addition of 10 nM and 100 nM of SA increases the amount of rubber produced in a significant manner See FIG. 7. The effect of exogenous 10 nM SA on one month old guayule plants grown in the soil under greenhouse conditions is also examined 50 ml of 10 nM SA solution of water and 0.0005% ethanol is administered to the soil twice weekly for two months and results in significant differences in the height and primary stem diameter relative to mock or water treated G7-11 plants (FIG. 8). The qRT-PCR results of PaAOS from the SA treated plants also show low expression pattern. The rubber content in the SA treated plants slightly increases and significantly differs compared to the mock treated G7-11 plants (FIG. 8). These data demonstrate that guayule's rubber content is increased by exogenous addition of SA to the plant.

Example 9 Transcription Factor Overexpression Results in More Rubber Production

PaAos promoter sequence is obtained (SEQ ID NO: 18) and is analyzed for transcription factors' binding sites using PlantPAN2.0 software (plantpan2.itps.ncku.edu.tw). The binding sites of a number of transcription factors, including WRKY3, WRKY71, MYBS3, CBF, and FLC, are identified. See FIG. 11A-11C, and Chen, et al., BMC Genomics 12:85-97 (2012). The Hevea nucleotide sequences of WRKY3, WRKY71, and MYBS3 are used to identify the DNA sequence of these three transcription factor genes in P. argentatum by searching for high percent identical sequences in a P. argentatum EST database in NCBI (using a computer algorithm, “BLAST”) and also in a newly assembled guayule genome (unpublished).

Based on the sequence information obtained from the sequence comparisons, RT-PCR forward primers and reverse primers are designed to amplify partial coding sequence of guayule's WRKY3-like (SEQ ID NOs: 19 and 20), WRKY71-like (SEQ ID NOs: 21 and 22), and MYBS3-like (SEQ ID NOs: 23 and 24). FIG. 12 contains these sequences as well as the annealing temperature and amplicon's size. These primers are used in the following protocol to isolate the coding sequences of the indicated transcription factors.

Approximately 150 mg stem tissue (4 stem tissues) are cut from guayule plants grown in tissue-cultured, placed into 2 mL tubes, and snapped-frozen in liquid nitrogen. Mortar and pestle are used to pulverize the tissues into a fine powder. RNA is extracted, quantified, and cleaned up using the protocols describe above in Example 2. Using the RNA isolated from the stem of wild-type guayule (line G7-11) and genetically altered guayule (i.e., pND6, pND6-AOSiL and pND6-AOS lines described above) cDNA is generated using iScript cDNA synthesis kit (Bio-Rad, Hercules, Calif.) using manufacturer's recommended protocol for semi-quantitative PCR and real-time quantitative PCR (qRT-PCR). An amount of 1 μg of RNA is used in the 20 mL reaction mixture. For PCR and qRT-PCR, 2 μL of the diluted cDNA (1:20) is used in a 25 μL and 15 μL reaction mixture, respectively. PCR is carried out in 25 tit of a mixture containing Taq 2× Master Mix (New England Biolabs, Ipswich, Mass.). After heating the samples to 94° C. for 2 minutes, the reaction proceeded with 40 cycles of 94° C. for 30 seconds, 58° C. to amplify the PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like in the above mentioned guayule lines for 30 seconds, and 68° C. for 1 minute. A final elongation step is carried out at 68° C. for 5 minutes. PCR products are separated by electrophoresis on a 1% (w/v) agarose gel; the expected PCR fragment is excised from the gel and purified with QIAquick® Gel Extraction Kit (Qiagen, Germantown, Md.) and sent to Elim Biopharmceuticals (Hayward, Calif.) for sequencing. In the qRT-PCR volume, 7.5 mL of iQ SYBR® Green Supermix is used (Bio-Rad, Hercules, Calif.). The qRT-PCR is run using the 7500 Fast Real-Time PCR system (Applied Biosystem, Waltham, Mass.) with the following thermal cycle: 95° C. pre-incubation for 3 minutes; amplification is performed for 40 cycles at 95° C. for 15 seconds and at 60° C. for 30 seconds; the dissociation stage is set for 95° C. for 15 seconds, at 60° C. for 1 minute, and at 95° C. for 15 seconds. Each qRT-PCR run is performed with three independent tissue samples, each sample having two technical replicates. The PaAos and 18S genes are used as internal controls. The primers used for each sequence, PCR annealing temperature, and the expected amplicon size are listed in FIG. 12. Crossing point value, which is the point at which the fluorescence crosses the threshold, and melting curve analyses are noted. The melting curve data are collected for all genes to ensure a single peak, indicating amplification of a specific region by a pair of primers. The relative expression values are calculated using the 2(-Delta C(T)) method (see Livak and Schmittgen (2001) supra). As seen in FIG. 13A-13C, the transcriptional expression of each of the three transcription factors (PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like) increases by a factor of 2- to 10-fold, compared to empty vector (pND6) or non-altered controls (18S gene and PaAos). The expression of the PaAos and the content of AOS protein on rubber particles, are reduced for lines overexpressing these transcription factors. Rubber content in guayule overexpressing these three transcription factors is increased by a factor of 2- to 10-fold compared to empty vector or wild type controls.

Plasmids are prepared to overexpress PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like in guayule. The cDNA sequence of each transcription factor is cloned into plasmid pND6 shown in FIG. 1 and replaces GUS. The primers used to generate and amplify PaWRKY3-like, PaWRKY71-like and PaMYBS3-like cDNAs are designed from the cDNA sequence obtained from guayule genome database assembly. The restriction enzymes AflII and B amHI are used for insertion of the the cDNAs into pND6 as described above in Example 1; thus primer pairs SEQ ID NOs: 27 and 28; 29 and 30; and 31 and 32, respectively are used to generate the cDNAs with the desired restrictions sequences. The PCR cycle program is 94° C. for 2 minutes (initial heating step) and PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like are independently amplified at 40 cycles of 94° C. for 30 seconds (denaturation), 58° C. for 1 minute (annealing) and 68° C. for 1 minute (extension) and an additional 5 minutes extension at 68° C. The resulting amplicons are purified and subcloned into pGEM T Easy vector (Promega, Madison, Wis.) using the manufacturer's recommended protocol and sequenced to confirm the sequence of the plasmids. PaWRKY3-like genomic sequence is SEQ ID NO: 39 and coding sequence is SEQ ID NO: 40. PaWRKY71-like genomic sequence is SEQ ID NO: 41 and coding sequence is SEQ ID NO: 42. PaMYBS3-like genomic sequence is SEQ ID NO: 43 and coding sequence is SEQ ID NO: 44. The PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like amplicons are digested with AflII and B amHI (Promega, Madison, Wis.) using the manufacturer's recommended protocol and are inserted into pPZP200 (Hajdukiewicz, et al. (1994)). As described above in Example 1, the PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like amplicons replace GUS in pND6 to generate pND6-PaWRKY3-like, pND6-PaWRKY71-like, and pND6-PaMYBS3-like. Agrobacterium EHA101 competent cells are transformed with one of each of these plasmids using the protocol described above in Example 1.

The transformed Agrobacterium EHA101 harboring either pND6, pND6-PaWRKY3-like, pND6-PaWRKY71-like or pND6-PaMYBS3-like are used to transform guayule G7-11 using the protocols set forth above in Example 1. See, also, Dong, et al. (2006) and Dong, et al. (2013). The transformed cells in the leaf strips are induced to grow using the protocols set forth above in Example 1. The shoot tips of the rooted plantlets are maintained or planted, as described above in Example 1. While the genetically altered guayule are growing in tissue culture under selection, the genetically altered plants are screened for integration of the expression vectors, pND6-PaWRKY3-like, pND6-PaWRKY71-like and pND6-PaMYBS3-like using the protocol described above in Example 1.

PCR is performed in 50 tit mixture containing Taq 2× Master Mix (New England Biolabs, Ipswich, Mass.), 200 ng guayule genomic DNA or 20 pg plasmid DNA, and 100 ng of pND6-WRKY3-like, pND6-WRKY71-like and pND6-MYBS3-like specific primers; namely SEQ ID NOs: 33 and 34; 35 and 36; and 37 and 38; respectively, (see also FIG. 12) for guayule transformed with pND6-WRKY3-like, pND6-WRKY71-like and pND6-MYBS3-like. After heating the samples to 94° C. for 2 minutes, the reaction proceeds with 35 cycles of 94° C. for 30 seconds, 71° C. to amplify the DNA for 30 seconds, and 68° C. for 1 minute. A final elongation step is carried out at 68° C. for 5 minutes. PCR products are separated by electrophoresis on a 1% (w/v) agarose gel. The band for the overexpression lines are about 800 bp, about 550 bp and about 400 bp for pND6-WRKY3-like, pND6-WRKY71-like, and pND6-MYBS3-like, respectively. The genetically altered guayule plants harboring the empty plasmid (pND6 (negative control)) are confirmed by GUS staining using the protocol described above in Example 1.

Genetically altered guayule containing intact PaWRKY3-like, PaWRKY71-like, PaMYBS3-like, and genetically altered guayule containing the control plasmid (pND6) are further screened to determine the RNA level using the protocols described above in Example 2 and FIG. 12. Collection of tissues, extraction, clean-up and quantification of RNA and cDNA synthesis are performed using the protocols described above in Example 2. Genetically altered guayule lines that overexpress PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like genes significantly more than controls are then selected for further analyses, as described below.

Genetically altered guayule lines that overexpress PaWRKY3-like, PaWRKY71-like, or PaMYBS3-like and non-altered guayule are grown as described in Example 3, above, and rubber content is assessed using the protocols described in Example 3, above. The average rubber content of the shoots of the genetically altered guayule lines for PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like are determined as described above. The genetically altered guayule lines containing PaWRKY3-like, PaWRKY71-like, or PaMYBS3-like are transplanted into soil and grown in the conditions described above in Example 3. The average rubber content of the shoots and roots of the genetically altered guayule lines PaWRKY3-like, PaWRKY71-like, and PaMYBS3-like are determined as describe above. Next, the quality of the rubber produced by the genetically altered guayule lines containing PaWRKY3-like, PaWRKY71-like, or PaMYBS3-like are assess using the protocols described above in Example 7. For these experiments, the plant biomass, rubber content, and quality are similar to or higher than the PaAosiL genetically altered guayule described above.

The foregoing detailed description and certain representative embodiments and details of the invention have been presented for purposes of illustration and description of the invention. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. It will be apparent to practitioners skilled in the art that modifications and variations may be made therein without departing from the scope of the invention. All references cited herein are incorporated by reference. 

We, the inventors, claim as follows:
 1. An altered guayule, parts and progeny thereof, that produces more rubber than an amount of rubber produced by a non-altered guayule comprising an alteration that causes said altered guayule to produce an increased amount of rubber, said alteration being an increase in amount of salicylic acid within said altered guayule; wherein said alteration causes said altered guayule to produce more rubber than said amount of rubber produced by said non-altered guayule.
 2. The altered guayule of claim 1, wherein said increase in said amount of salicylic acid within said altered guayule comprises administering salicylic acid to a guayule to generate said altered guayule; and wherein said salicylic acid causes said altered guayule to produce more rubber than said amount of rubber produced by said non-altered guayule.
 3. A germplasm of said altered guayule of claim 1, wherein said germplasm comprises said alteration.
 4. A seed of said altered guayule of claim 1, wherein said seed comprises said alteration.
 5. A method for increasing an amount of rubber produced by an altered guayule compared to an amount of rubber produced by a non-altered guayule, said method comprising an alteration, the alteration being increasing the amount of salicylic acid within said altered guayule, wherein said alteration causes said altered guayule to produce more rubber than said amount of rubber produced by said non-altered guayule.
 6. The method of claim 5, wherein said increasing said amount of salicylic acid within said altered guayule comprises administering salicylic acid to said guayule to generate said altered guayule; and wherein said salicylic acid causes said altered guayule to produce more rubber than said amount of rubber produced by said non-altered guayule.
 8. The method of claim 5, further comprising exposing said altered guayule to between approximately 7° C. and approximately 15° C. for approximately 8 hours per day.
 9. An altered guayule produced by the method of claim 5, wherein said altered guayule comprises said alteration and produces more rubber than the amount of rubber produced by a non-altered guayule.
 10. An altered seed of an altered guayule produced by the method of claim 5, wherein said altered seed comprises said alteration. 